THE PHYSIOGRAPHY OF THE COX RIVER BASIN. http://www.biodiversitylibrary.org/item/108641#page/338/mode/1up

By Fbank a. Ckaft, B.Sc, Caii'd Scholar in Geography and | 

Science Research Scholar, University of Sydney. ' ; 

(Plates xix-xx, and seventeen Text-figures.) 

[Read 30th May, 1928.] 

Introduction. 

Area dealt with ; Previous work and literature ; General considerations. 

Classification of Regions. 

Blue Plateau ; Jenolan Plain or Plateau ; Wallerawang and Lithgow valley levels ; 

Kanimbla and Megalong Valleys ; Jamieson's Valley and the Kowmung Basin ; The 

Monadnocks. 

Geology of the Area. 

Main structural features ; Ancient ranges and peneplains ; The rocks, and Their 

resistance to erosion. 

Dominant Physiographic Features. 

Blue (Mt. ) and Jenolan Plateaux; Kanangra Platform; Wallerawang and Lithgow 

Valleys ; 

Boyd and Budthingeroo Creeks ; 

Retreat, Tuglow and Fish Rivers ; 

Kanimbla and Megalong Valleys ; 

The relationship between the Kanimbla and Wallerawang  Levels ; 

Jamieson's Valley and the Kowmung Basin ; 

Valleys of the Lower Cox- WoUondilly ; 

The Warragamba Gorge. 

Main Folds and Warps of the Area. 

General considerations of the folding ; The Mulgoa Step ; The Kowmung Warp ; 

Extent and external relationships of the Kowmung Warp; The old Blue (Mt. ) 

Anticline ; Direction of forces causing uplift. 

Streams of the Area. 

Stream Characteristics and Relationships; Divides of the Cox (Solitary Creek; 

Bindook Swamp) ; Cox River and its Tributaries (Relative stream ages; Anomalies 

of direction); Relationship between the Kowmung and Wollondilly ; History of the 

stream system. 

Past History of the Area. 

Earth Movements ; Stream History. 

References. 

Introduction. 

This paper treats of the rough Blue Mountain Plateau, a good deal of which is 

very little known. It commences with an examination of topographic features, 

and the influence of rock structure on these is traced. It is then possible to 

divide the area into a number of small parts according to form and development

of surface features. The evolution of each part is traced, and the parts 

correlated. In this way the earth movements which have affected the area are 

discovered and explained. In the light of the knowledge thus obtained the 

development of the stream system is traced, and the past physiographic history 

of the area is outlined. 

The research work which this paper describes was undertaken during 1926 

under the supervision of Professor Griffith Taylor, to whom my thanks are due 

for his great interest in the work, and for many suggestions of his which are 

embodied in this paper. Much of its merit is due to him, and to his continual 

encouragement. Next, I have to thank Miss W. Riley, of Leura, for most of the 

printing on the diagrams. Messrs. H. C. Allen, B.Sc, and C. H. Black, B.Sc, 

assisted in the work on Jamieson's Valley in very bad weather, and I owe a great 

deal to them. The Water Conservation and Irrigation Commission has also 

supplied a valuable map and other information. 

Text-Fig. 1.— The Cox River Basin. 

Block Diagram of the Area. This summarizes the topography. The plateau 

masses are trenched by narrow gorges and valleys on the south and east, whilst 

broad, mature valleys, which are now being trenched by the streams, are found 

in the centre and north of the area. The great Kowmung Canyon is very striking. 

My very sincere thanks are also due to many residents of the area who 

assisted me in a variety of ways. I would like to mention particularly Messrs. 

Bulkeley (Wallerawang) ; Kirby and Carlon (Megalong) ; Maxwell and Kill 

(Kedumba or Jamieson's Creek) ; and James and Kerswell (Lower Burragorang) ; 

together with their wives and families. Many others have also earned my hearty 

thanks, and I would pay a tribute to their kindness and helpfulness, without 

which it would have been impossible to examine all the area which is here 

described. 

Area dealt with. — In this paper, the Cox River Basin is taken to include that 

area of country drained by the Cox and Kowmung Rivers and their tributaries, 

together with the Warragamba and Lower Wollondilly Rivers. The latter streams 

are included because the problems associated with them are intimately related 

to the problems presented by the Cox. This embraces an area of some 1,600 

square miles. 

Previous work and literature. — The area has not been treated previously, as  a whole, in any detail. 

Mr. Andrews and Professor Griffith Taylor have written  valuable papers on the general physiography of the area, 

and intensive research  tends to prove many of their theories. The geology of the country adjacent to 

the Main Western Railway and the Lithgow Coalfield is fairly well known, but  the geology of the rough 

Kowmung, Kanangra and Jenolan River basins, and  Mt. Mouin district has not been studied. 

Some observations on this phase of the  subject are embodied in the paper. 

General considerations. — The Cox River area includes some of the wildest and  most broken country 

in this State; and has, since the earliest days of white  settlement, proved to be a great obstacle in the way of 

free communication  between Sydney and the interior — not so much on account of the altitude  involved, 

but because of the profound recent dissection of a moderately uplifted  surface. The great gorges which the 

main streams have cut have, in general,  a north-south trend across the radial lines of communication from 

the Sydney  Basin, and only where persistent east-west ridges occur, as in the case of the 

Glenbrook-Clarence watershed, is the relatively easy construction of roads and  railways possible. 

Classification of Regions. 

A study of the Block Diagram (Text-fig. 1) will show that the area includes  a number of dissimilar 

physiographic types. The streams of the Upper Cox flow  to the east in broad, flat valleys which have, 

however, a general outlet to the west,  into the Macquarie basin. The Middle Cox basin consists of a series 

of broad,  flat valleys which have been trenched by deep juvenile gorges; whilst the Lower 

Cox and its associated streams flow from the wide valleys into deep, narrow  trenches, finally debouching on 

the plains of the Sydney Basin, Thus the area  appears to fall into a number of well-defined natural regions, 

which are determined  mainly by differences of elevation. There are six of these regions, which vary  notably 

from one another, and whose characteristics will now be described. 

(i). The Blue Plateau. — In this paper, the term "Blue Plateau" will be used  in a restricted sense. The plateau 

extends from the Hunter River Valley in the  north to Lake George in the south and can, in a general sense, be 

described as a  topographic unit and have the name "Blue Plateau" applied to it. Here, however,  the term will be 

used to designate that elevated sandstone block which in parts 

rises to 3,500 feet above sea-level, and occupies all of the northern and eastern  parts of the area, together with the 

lower warped country leading up to it.  This region has three well-marked subdivisions, viz.. the lower or Mulgoa 

"step",  extending from Glenbrook to the south of The Oaks; the King's Tableland "step", 

extending from Hazelbrook in the north away beyond Oakdale in the south, 

including the country to the east of Jamieson's Creek and the Lower Wollondilly; 

and the main plateau, varying from 3,000 to 3,500 feet in elevation, and extending 

westwards from a line joining JCatoomba with Mounts Hay, Tomah, Wilson and 

Irvine. Between these steps are stretches of uniformly-sloping land. This plateau 

is essentially a recently-warped peneplain, and is deeply dissected in parts. 

(ii). Jenolan Plain or Plateau. — This region consists mainly of soft Silurian 

rocks. It is about 700 feet higher than the main mass of the Blue Plateau, whose 

average elevation is about 3,300 feet. The Jenolan Plateau extends vertically from 

3,700 to 4,400 feet above sea-level, having an average elevation slightly in excess 

of 4,000 feet. Its surface is generally very level, but is trenched in the east and 

north-east by deep gorges. This plateau extends from Sunny Corner south- 

eastwards to Kanangra Walls, and westwards to the Stony Ridges near Bathurst. 

(iii). Walleratcang and Lithgow Yalley Levels. — The area of flat late mature 

valleys at an elevation of 3,100 feet centring on Wallerawang comes under this 

heading, and includes the Lithgow, Portland, Wallerawang and Solitary Creek 

Valleys, together with similar higher valleys to the south, on Boyd Creek and 

the Upper Tuglow, for example. It will be seen, from the outset, that these 

valleys are cut in a variety of rocks. 

(iv). Kanimbla and Megalong Valleys. — The middle course of the Cox, between 

Lett River and the Narrow Neck-Gangerang Range line, is marked by a great 

series of upland valleys. These occur at elevations varying from 1,900 to 2,500 feet, 

having an average elevation of 2,200 feet. The valley floor is geologically varied, 

consisting of granite, conglomerate, sandstone, and certain slates, etc. The 

valley itself contains some alluvial deposits to the north of the Cox, and is, 

physiographically, of great interest. On the eastern margin, the river leaves the 

valley by a great canyon which is, for nineteen miles, nowhere less than 2,000 

feet deep. 

(v). Jamieson's Valley and the Kowmung Basin. — Jamieson's Valley and the 

Kowmung Basin form a great oval-shaped valley, which is divided into two parts 

by the Cox River. The river does not, however, destroy the unity of the feature. 

The lower part of Jamieson's Valley is only 500 feet above sea-level, but a steadily- 

rising warped surface extends to the west, south-west and south of the small 

stream flats, rising to 2,300 feet on the Megalong level at Megalong Gap; and to 

2,800 feet at Bindook Pass, on the southern divide of the Kowmung. The uniform 

warped valley floor is trenched by the Cox and Kowmung Rivers. The warping 

affected the mouth of Jamieson's Creek in a manner which will be discussed 

later. 

(vi). The MonadnocTis. — Rising above the respective surfaces of the plateaux 

are a number of monadnocks and residuals. These may be classed under two 

headings — the basalt residuals and the quartzite blocks. The former occur mainly 

along the southern divides of the Kowmung, and include Mounts Werong, Colong 

and Shivering, South Peak (Yerranderie), Harvey's Mount and a large area 

around Shooter's Hill. The old quartzite peaks are Mounts Walker, Flaherty, 

Bindo, Lambie and the Gangerang Range. The former appear to be relics of an 

ancient peneplain, but the latter are monadnocks that have existed through long 

periods of geological time on account of their great resistance to erosion. They 

are discussed more fully in other parts of the paper. 

Geology of the Area. 

Main Structural Features. — The rocks of the area are divisible into two main 

classes, namely, 

(i) Mesozoic and Upper Palaeozoic and 

(ii) Lower Palaeozoic. 

The former occupy the northern and eastern parts of the area; the latter occur 

in the centre, south-west and west. The Triassic and Permian beds (Hawkesbury 

and Narrabeen Series, Upper Coal Measures and Upper Marine Series) rest 

unconformably upon the older strata, and there is a definite line of demarcation 

between the present outcrops of the two. This line runs, roughly, along the 

Kowmung Valley, across the Cox, and on the northern side of Kanimbla Valleys. 

The area to the west of the line would thus appear to have had a predominantly 

upward movement since Devonian times, whilst the country to the north and 

east would appear to have been an area of relative depression. Thus some of the 

earth movements which are postulated in this paper appear to be renewals of 

these ancient earth movements, as the south-west (Jenolan Plateau) has under- 

gone greater recent elevation than the remainder of the area. 

Text-fig. 2. — Geology of the Cox Basin. 

The eastern and north-eastern parts are very much younger, geologically, than 

the western portion. The former represent the old regions of relative depression, 

whilst the latter represent areas of long-continued relative uplift. 

The geological structure is thus readily understood (Text-fig. 2). Various 

outliers of the newer rocks are found on the older, higher rocks of the Jenolan 

Plateau; and these shed light, not only on the past geological history of the area, 

but also upon recent warping movements that have affected it. Two groups of out- 

liers may be particularly noted — those along and adjacent to the Main Divide 

between Rydal and Jenolan, and those to the east of Kanangra Creek. 

The first group consists of a series of outcrops strung out along the Main 

Divide between Rydal and Hampton, along some of the ridges running north 

and south from the Divide, the most notable being between Lowther and Hartley. 

The relics belong to the Upper Marine Series, and consist mainly of sand- 

stone and conglomerate. They rise from 3,100 feet near Rydal to 3,950 feet three 

miles to the north of Hampton, and 4,200 feet about three miles to the south- 

east of Jenolan Caves. At Hartley these rocks are found as low as 2,400 feet, but 

they rise 1,400 feet to Hampton, which is twelve miles distant at 3,800 feet. 

The most interesting member of this group is that outlier which is found 

three miles to the north of Hampton. It stretches for two miles along the Main 

Divide, and attains a maximum thickness of 350 feet. It consists of conglomerate, 

shale, sandstone and, at the top, a bed of grey shale containing a six-inch band of 

coal. The latter is found right on the crest of the ridge, 3,950 feet above sea- 

level. The highest outcrop of coal on the western coalfield is at 3,200 feet at 

Piper's Flat, so there is a difference in elevation between the two of the order of 

750 feet. This represents the extra amount of elevation which the Hampton beds 

have suffered compared to the corresponding rocks of the main Blue Plateau around 

Wallerawang; it is also equal to the difference in elevation between the Blue and 

Jenolan Plateaux. 

Warping of the country between Hartley and Hampton must certainly have 

taken place unless one is prepared to assume that the conglomerate beds could 

have been laid down at and along the present slope, which is approximately 120 

feet per mile. 

The second series of outliers occurs to the east of Kanangra Creek, at 

Kanangra Walls and along the Gangerang Range. The newer sandstone is 

horizontal, and rests unconformably upon the older folded beds. Kanangra Walls 

are formed by the weathering of this rock along a major joint plane. The sand- 

stone, whose upper surface is at 3,300 feet, attains a maximum thickness of 250 

feet, and extends northwards along the eastern side of the Gangerang Range, 

appearing as a broken bench on the side of the high quartzite residual, which 

rises to 3,700 feet. 

The age of this sandstone is doubtful. On the Geological Map of N.S.W., 

1914, it is marked as belonging to the Upper Coal Measures. It extends at the 

3,300 feet level along Gangerang Range, and appears to correspond to the Hawkes- 

bury Series on Narrow Neck, Katoomba, at 3,400 feet. The presence of a coal 

band and the reputed occurrence of Glossopteris indicate that it does not belong 

to the Hawkesbury Series. The difference of elevation of 600 feet between this 

and the Hampton rocks may be remarked on as a sign of differential uplift. 

Ancient Ranges and Peneplains. — From very early times the crust of the 

earth in this area has been in a state of unrest. The Silurian and Devonian beds 

are unconformable, and have been greatly crushed and folded. Since the close of 

the Carboniferous there has been relatively little folding, the earth movements 

having been more of a vertical character. 

The geological history of the area opens with the Silurian sedimentation, 

when an extensive series of limestones, shales and interbedded volcanics, with 

subsequently-metamorphosed slates, was formed. A period of uplift and erosion 

was followed by further downthrust and sedimentation in the Devonian period. 

The Devonian beds are now of a predominantly metamorphic character, consisting 

of quartzites, slates, shales, and intrusive porphyries. 

At the c lose of the Devonian there was a great period of mountain-building, 

accompanied by the intrusion of a batholith of granite, quartz-porphyry dykes, and 

regional metamorphism. The country was intensely folded into a series of 

symmetrical synclines and anticlines, the relics of folding being still plainly 

visible. With the movement of uplift dominant, the land was kept above the sea, 

and a great cycle of erosion resutlted in the reduction of the folds, and the 

formation of a peneplain. So great was the amount of erosion, that areas of the 

intruded granite were exposed. The harder rocks, such as Gangerang and Mt. 

Walker, persisted as peaks, up to 2,000 feet above vhe softer rocks of the pene- 

plain, which formed gently-rolling plains. Some of the peaks exist at the present 

time. 

At the close of the Carboniferous, a downward movement of the land inter- 

rupted the cycle of erosion. This movement was more intense in the east, and 

hardly affected the western part of the area. The Upper Marine beds and Upper 

Coal Measures were laid down unconformably on the upturned eroded edges of 

the slates, and quartzites, and on the granites. Until the close of the Triassic, the 

eastern part of the area continued to be depressed, but the western part appears 

to have been lifted above the sea at the close of the Permian. Since the deposition 

of the Hawkesbury, Narrabeen and Wianamatta beds — the latter only occurring on 

the eastern margin of the area — the major movement has been one of uplift. The 

earliest uplifts have all been obscured by those coming subsequently, and it is 

not until the period of basalt flows, probably later than Middle Tertiary, that we 

get a distinctive peneplain preserved. This is now represented mainly by isolated 

basalt areas and caps, a few of which, e.g.. Mounts Colong, Shivering, Werong, 

Clarence, and the country near Shooter's Hill, are found in this area. 

The great Tertiary Peneplain, which now forms the plateau surface, was 

probably formed in the latter part of the Tertiary period. The history of the land 

surface subsequent to this peneplanation, is most readily traced by physiographic 

methods. 

The Rocks, and their Resistance to Erosion. — Reviewing the rock structures 

of the area, one is struck by the great resistance to erosion shown by the majority 

of the rock types. The younger sedimentary rocks — Triassic and Permian — are 

here near their western limits, and so consist mainly of sandstones, grits and 

conglomerates. The Hawkesbury Sandstone and Narrabeen beds are here prac- 

tically all sandstone and grit, with only thin bands of shale. In general the Upper 

Coal Measures are soft, consisting of shales and crumbling sandstones, as in 

Jamieson's Valley and around Lithgow. Nearer their periphery they, too, are 

very hard. To the north of Piper's Flat the surface of the Blue Plateau is of 

hard Coal Measure sandstone (containing Glossopteris) . On Mt. Mouin, and the 

ridge to the south-west of Yerranderie, these series consist mainly of resistant 

grits. At Wallerawang and Marangaroo also the basal beds — the Marangaroo 

Conglomerate — are very hard, forming cliffs where softer shale bands are cut 

away from beneath them. 

The Upper Marine beds are also, in general, very resistant to weathering in 

such places as the Kanimbla and Wallerawang districts, where conglomerate and 

sandstone are predominant. To the east, as in Jamieson's Valley, a considerable 

thickness of shale and tuff also occurs. The basal deposits often contain small 

deposits of alum. In parts, as in Megalong, there are bands of pebbles in a 

crumbly matrix, in which this alum is found. On the whole, the Upper Marine 

Series is very resistant to erosion in the west and south, and moderately resistant 

in the north-east. 

The older rocks are principally igneous and metamorphic. Of these, the 

Devonian slates and quartzites are uniformly hard, whilst the Silurian slates 

and shales are much softer. One particular bed of the Devonian series, a white 

glassy quartzite which occurs on Gangerang Range and Mt. Walker, is particularly 

resistant. Practically the only natural means of disintegration is by the freezing 

of water in joint and bedding planes, which splits the rock up into cubes, with 

edge up to a foot, and which litter the mountain sides. The Devonian slates, 

too, are hard. On Breakfast Creek, for example, there has been no appreciable 

differential erosion in the slates and quartzites. The Silurian slates and shales 

are soft, giving a subdued topography, as on the uplands near Jenolan Caves, 

and forming characteristic saddle ridges as on the Kowmung-Wollondilly divide. 

The roots of falling trees, blown over by the wind, tear great holes in these rocks, 

which are generally strongly jointed and laminated. Despite the softness of its 

rock types, the Jenolan Plateau stands up as a high block, and so cannot be a 

mesa, or relic of a separate peneplanation older than that of the Blue Plateau. 

The granites of the Cox Valley vary in hardness from place to place, but are 

generally not very resistant to erosion, on account of their susceptibility to 

chemical weathering. Where caps of Upper Marine sandstone occur in the valley, 

hills are found; but where the sandstone has been worn away, the granite is 

quickly eaten down, forming typical rolling hills. Above Galong Creek (Megalong 

Valley) for instance, the Cox is entrenched in undulating granite hills. Below 

this stream it flows into an extremely steep-sided ravine of Devonian strata. A 

small boss of granite is exposed on the Lower Cox below Jamieson's Creek. 

The rocks can thus be classified in descending order of resistance to erosion 

as follows: — 

i. Devonian quartzite and indurated conglomerate (latter on Jamieson's 

Creek). Basalt caps, 

ii. Hawkesbury and Narrabeen sandstones; Upper Marine sandstones and 

conglomerates; some Upper Coal Measure sandstone, 

iii. Devonian slates and intrusive porphyries, 

iv. Granites, in general. 

V. Silurian slates, shales, etc., in general. 

vi. Upper Coal Measures; interstratified shales in the Upper Marine, 

Hawkesbury, Narrabeen, and Devonian Series. 

Only the last two types are distinctly soft. It will be seen that the great 

mass of soft rocks on Jenolan Plateau lies away from the great Cox and Kowmung 

Valleys, which have been cut in almost uniformly hard rocks. The effect of this 

has been to reduce differential erosion to a minimum in the formation of the 

broad valleys. 

Dominant Physiographic Features. 

Blue (Mt.) and Jenolan Plateaux. — The Blue Plateau has been recognized by 

geographers and physiographers as part of an uplifted and dissected peneplain. 

Mr. Andrews originally regarded the Jenolan Plain as a relic of a more ancient 

cycle of erosion than that which formed the Blue Plateau (Geography of Blue 

Mts.), but has since modified his views on the subject in general. He says (Geog. 

Unity of Eastern Australia, pp. 433-434) : "It would appear, in fact, that wherever 

in Eastern Australia two unreduced plateau masses exist side by side at variable 

altitudes, a fault or sharp fold separates them". And again, "The same horst (i.e., 

west of Burragorang) exceeds 4,000 feet a few miles east of Bathurst, and the 

Bathurst Plains (2,500 feet) appear to be a senkungsfeld dropped between Orange 

and the Sunny Corner Highlands". There appears to be strong field evidence 

in support of these views. 

The peneplain as an Australian feature is discussed by Dr. Fenner (Physio- 

graphy of Werribee Area, p. 203, ct seq.). He, in common with many other writers, 

whom he quotes, holds that the Tertiary peneplain is the dominant feature of the 

Australian highlands. The uplifted and dissected peneplain is represented in this 

area by the Blue and Jenolan Plateaux. 

There are two main lines of evidence which seem to indicate that these two 

surfaces belong to the same cycle. Firstly, there is the relative hardness of the 

two masses. The surface of the Blue Plateau is composed of hard sandstones, 

but the Jenolan Plain is mainly composed of soft shales and slates. The presence 

of these rocks has resulted in very subdued topography in regions as yet 

unaffected by headward erosion caused by the upwarping of the plateau, the 

country around Hampton being typical of this. If the Jenolan Plain were a 

mesa, or relic of a one-time complete peneplain, one would expect the rocks of 

which it is composed to be hard and resistant to erosion. This, however, is not the 

case. There is evidence, both geological and physiographic, of recent differential 

uplift of the Jenolan Plain above the Blue Plateau. The latter has an elevation of 

3,300 to 3,400 feet, whilst the Jenolan Plateau has an average elevation of 4,000 

feet, varying from 3,800 to 4,400 feet; that is to say, the latter is, on the average, 

700 feet higher than the former. A certain amount of local differential uplift of 

the Jenolan Block itself is probable, as it exhibits a wavy surface. 

The greater elevation of the Jenolan Plateau is due to uplift which has not 

affected the Blue Plateau to the north and east. The outlier of Coal Measure rocks 

at Hampton, 700 feet above corresponding rocks at Lithgow, has already been 

noted. The only other explanation of this difference in elevation is an assumption 

that this rim of the coal basin saucer rises 700 feet in a few (7) miles, the direct 

distance between this outlier and similar rocks at South Bowenfels; which seems 

improbable, especially when considered in connection with the sandstone at 

Kanangra at 3,300 feet, just off the eastern margin of this Jenolan Plateau. 

There also appears to be topographic evidence of both warping and faulting 

on the southern side of Kanimbla Valley. On the northern side of the Cox are 

the Kanimbla levels at 1,900 to 2,500 feet. On the southern side there is a uniform 

slope from this height right up to the Main Divide at 4,000 feet, thus giving the 

Cox a valley which is asymmetric about the river; this slope consists mainly of 

granite, with a few outliers of Upper Marine rocks. There does not appear to 

be any obvious reason why this rock rises to 4,000 feet on the divide when it 

occurs in Kanimbla at 1,900 to 2,500 feet, and is there subhorizontal, other than 

that given by the explanation that these uniformly-sloping ridges were once 

more level than now, and have been tilted by warping, thus giving the Cox its 

asymmetric valley. The Upper Marine rocks were apparently deposited on a 

granite peneplain, formed during the long period of erosion succeeding the 

Kanimbla Epoch of mountain building; and it does not seem that these con- 

glomerates would be deposited along a steeply-sloping surface of fairly soft rock 

in such a position as that in which they are now found. In passing, it may be 

noted that the Kanimbla conglomerate, in common with the other Permian and 

Triassic strata, dips to the east, and an upward slope from north to south begins 

only to the south of the Cox, in the supposedly warped area. 

This slope of the southern ridges is also noticeable in the case of the Black, 

Jenolan, and Mini Mini Ranges. Below Galong Creek, there is a marked dis- 

continuity of slope in the Upper Marine beds as one goes from the north to the 

south of the Cox River. To the east of the River, the beds are practically 

horizontal, but on the western side they dip steeply northwards. The Cox flows 

a little to the south of this line of discontinuity, which may also be marked by 

slight faulting. There appears to be a slight vertical displacement here, but this 

cannot be definitely asserted. 

Text-flg. 3.- — Physiographic Fault at Kanangra Walls. 

This fault is a revival of the old fault lines noted in Text-flg. 2, between the 

rising area to the west and the sinking area to the east. Kanangra Canyon is 

cut along this fault. 

On the east the Jenolan Plateau is bounded by a definite scarp, which, 

although hardly recognizable as such in places, owing to confusion with the 

western margin of the Kowmung basin, is, nevertheless, fairly well defined 

(Text-fig. 9C). Perhaps the best place for observing this scarp is from the edge 

of "Big Plain" (4,000 feet), which is situated on the Kowmung- Wollondilly divide, 

about three miles to the west of Mt. Shivering. To the east of the plain, along 

the dividing ridge, the land falls away steeply to 3,500 feet near the Mount, and 

thence, in a series of steps, to Bindook Swamp, at an elevation of 2,800 feet, 

which is some 300 feet below the surrounding country. Away to the north, a 

low scarp can be seen rising above the level of Kanangra Walls (Text-fig. 9C). 

This scarp rises to 4,300 feet, and forms the eastern edge of Jenolan Plateau. 

Between "Big Plain" and Kanangra Walls the scarp is much cut up, being trenched 

by great juvenile gorges. 

On the west, the Jenolan block appears to be bounded by a definite scarp, part 

of which is the Stony Ridges to the east of Bathurst, as Andrews (1910) points out. 

From these considerations it appears that the Jenolan Plateau is composed of a 

broad, dome-shaped warp, which has been faulted along its north-eastern, eastern 

and southern edges. 

I do not propose to describe the Blue Plateau in detail, as its salient features 

are already fairly well known. It consists of portion of an upwarped, slightly 

dissected peneplain, which is being trenched by stream action, resulting in the 

formation of deep, narrow canyons. A part of this has been described by Taylor 

(1923a). The plateau does not rise uniformly from east to west (Text-fig. 12), 

but, as Taylor points out, it exhibits "Steps" or "Treads", one at Mulgoa and one at 

Hazelbrook, both of which are very definite. Their respective elevations are 500 

and 2,200 feet. The main change of slope occurs along a north-south line which 

runs through Katoomba, Mts Hay, Tomah and Wilson. To the east of this line, 

the average grade of the warp slope is of the order of 125 feet to the mile. To the 

west of this line, however, the slope rarely exceeds 20 feet to the mile. On the 

west of this line, therefore, the true plateau surface is found. Whilst these steps 

may be due to differential warping during a single period of uplift, their occurrence 

is not inconsistent with the theory, suggested by Taylor, that the present plateau 

surface has been formed by a series of non-contemporaneous warps and folds, 

and represents the algebraic sum of the same. This view has also been held by 

Mr. Andrews and the late Mr. Hedley. * 

The Kanangra Platform.- — The two plateau levels are found in close proximity 

to one another at the head of Kanangra Creek, 20 miles to the south-east of 

Jenolan Caves, where the Kanangra "Platform" (Text-fig. 3) is located. Two 

main surfaces are found here, the upper being part of the Jenolan Plateau at an 

elevation of 4,000 to 4,250 feet, the lower level or Kanangra Platform having an 

elevation of 3,300 to 3,400 feet. The former consists of folded Silurian rocks, 

bevelled off across the bedding planes and granite, as on Boyd Creek. The mature 

upper valleys of Budthingeroo and Boyd Creeks are incised 300 to 500 feet in the 

plateau. The Kanangra Platform consists partly of horizontal sandstones, and 

partly of planed-off slates and quartzites. There is no change in slope or 

topography in the passage from one series to another. The upper valleys of 

Kanangra Creek are very little entrenched in this hard surface. Between these 

two levels there is a very definite scarp, 600 feet high, down which the road winds. 

It has hardly been cut into in this part by the small wet-weather streams. To 

the north, this scarp forms the western side of the great Kanangra Canyon. 

Kanangra Creek has taken advantage of the fault line, and has carved out a 

gorge which is 2,000 feet deep at the Walls, and somewhat over 3,000 feet deep 

between Gangerang Range and Mt. Guouogang. The streams plunge abruptly into 

this canyon from the platform in a series of high waterfalls, descending 1,500 

feet in a mile. 

218 

PHYSIOGKArHY OF THE COX RIVEK BASIN, 

To the south, the scarp consists largely of softer rocks, and has been deeply 

cut into by the powerful Kowmung streams, but it is still plainly discernible 

(Text-fig. 9(7). The 3,300 feet level is found along Gangerang Range on the 

eastern and northern sides. The peaks rise above this bench as monadnocks. 

Although approaching the Jenolan Plateau in elevation, Gangerang is a separate 

feature, and has only recently been made to appear comparatively low by the 

rise of the Jenolan block to the west of the fault. At Kanangra Walls therefore, 

the two plateau surfaces are found together, separated by a sharp fault. 

Comparatively recently, we conclude, the two surfaces were at the same level. 

The fault scarp continues south into the Wollondilly basin, but passes into a fold 

further to the north, in the Kanimbla Valley. 

THE — 

Text-fig. 4. — Contour Map of Wallerawang District. 

Note the mature valleys broken only by tlie ancient monadnocks of Mounts 

Walker and Flaherty, the entrenched meanders of the Cox, and the asymmetry 

of the valley of Piper's Flat. 

Wallerawang and Lithgoiv Valleys. — The upland valleys around Wallerawang 

and Lithgow form part of a valley system which extends across the Main Divide 

at Rydal and Piper's Flat, and includes the upper valleys of the Turon and Fish 

Rivers. In considering these valleys around Wallerawang, therefore, it is neces- 

BY F. A. CRAFT. 

219 

sary to remember that they are types of a valley-system which is not confined 

to the Cox basin. I propose to apply the name "Wallerawang Valley" to that valley 

about the 3,000 feet level which centres on Wallerawang, and extends from "Wolgan 

Gap and Portland to Rydal and Wallerawang. "Lithgow Valley" will be defined 

as the valley stretching from Lithgow to Marangaroo, with a branch extending to 

the east of Mt. Walker towards Rydal. 

The topography of these valleys and the associated plateau regions is clearly 

shown in the contour map (Text-fig. 4) and block diagrams (Text-figs. 5 and 7). 

The two valleys are actually continuous, but the monadnocks, Mounts Walker 

and Flaherty, which rise from 700 to 800 feet above the valley floor, divide it into 

two parts. 

Text-fig. 5. — The Head of the Cox. 

The broad valley of Piper's Flat Creek extends over the Main Divide into the 

Turon Basin. The southern margin has been affected by recent warping. The 

hard rocks of the plateau have been formed, by long continued erosion, into 

subdued ridges and mature valleys. 

Wallerawang Valley, on the western side, varies in elevation from 2,900 feet 

at Wallerawang to 3140 feet and 3150 feet at Piper's Flat and Rydal respectively, 

and 3,175 feet in Wolgan Gap. The width of the valley along Piper's Flat varies 

from two to four miles, and the average depth is of the order of 400 feet. The 

valley of Cox's Creek is narrower, but of the same general depth. In general 

character the Wallerawang Valley is mature and, in common with the surrounding 

plateau, geologically varied. The valley floor is composed of Upper Coal Measure 

shale. Upper Marine shale, sandstone, and conglomerate, Devonian shale and 

quartzite, and granite. The plateau consists of Devonian quartzites and shales, 

Upper Coal Measure shales and sandstones (the latter to the north of Piper's 

220 PHYSIOGRAPHY OF THE COX RIVEK BASIN, 

Flat), Hawkesbury sandstone, and granite. There has been little differential 

erosion between these rock types. 

There is a gentle uniform rise along Cox's Creek, for example, from Wallera- 

wang to Wolgan Gap, over Upper Marine, Upper Coal Measure and Hawkesbury 

rocks. The junction of different series cannot be detected by change of slope. A 

similar thing is true of ridges in this valley that run down towards Piper's Flat 

from the southern side. A traverse along the Main Divide to the south of Piper's 

Flat takes one over Upper Marine and Devonian rocks and granite. Again there 

is no notable change in topography with change in rock type. The hard sand- 

stones now found on the plateau to north and west of this valley once extended 

right across the valley, as the outlier of sandstone on Round Hill (3,720 feet) on 

the southern side of the valley shows. This mature valley cannot, therefore, 

be ascribed to differential erosion in rocks of varying hardness, but must be the 

result of prolonged erosion when the land surface was not far above base-level, 

before the main uplift which formed the present plateau. 

One of the most striking topographic features of the district is the asymmetry 

of the main valley, that of Piper's Flat Creek. The northern side of this valley, 

from Wallerawang to Portland, is a steep scarp against Avhose base the main 

stream flows. The southern side of the valley rises gently and uniformly, and is 

little cut into by the swampy streams that flow down it. The main stream 

receives no tributaries at all from the north, as the divide on that side is, in 

general, less than half a mile away. This feature has no apparent explanation, 

although there may have been a gentle uplift to the south, near Mt. Lambie, 

causing the stream channel to migrate northwards. 

The valley of Cox's Creek is not so large or important as the other branch of 

Wallerawang Valley. Near Wallerawang, it is two miles wide; four miles above 

the town, however, it is but a half-mile wide, and narrows further towards Wolgan 

Gap. The same stream, which is the largest single stream in the head valleys of 

Cox River, is very little entrenched in its valley. Indeed, in parts, its tributaries 

have no definite channels through the swamps. 

The streams of Wallerawang Valley differ somewhat in character. Cox's 

Creek and its tributaries run over swampy silt flats, and swing backwards and 

forwards over the valley. Piper's Flat Creek has a grade of about 30 feet to the 

mile, and is grading down its channel and cutting away the silt flats which it had 

previously deposited, which are up to a quarter of a mile wide. These silts are 

found along the tributaries up to four miles away from the main stream. On 

Thompson's Creek, for example, four miles from its mouth at Irondale, the silts 

are about 80 yards wide, and at least 10 feet deep, and are built up of peaty 

material at an elevation of 3,300 feet, 300 feet above the main valley. The 

streams are now just beginning to attack their head silts at 3,200 to 3,300 feet. 

These silts are found on most of the other tributary creeks of the valley, and on 

Solitary Creek, about two miles above Rydal. 

One of the most interesting features of the valley is the occurrence of a line 

of gravels along Piper's Flat, up to 50 feet above the modern silt flats, and up to 

30 feet thick. These gravels are found in a well-defined belt along the southern 

side of the valley (Text-fig. 6) extending over the Main Divide at least to the 

outskirts of Portland. Characteristic deposits may be seen near Wallerawang 

station and in the railway cuttings around Irondale. The pebbles vary in size 

from a couple of inches to a foot or more in length along the major axis, and are 

BY F. A. CItAFT. 

221 

ellipsoidal in shape. Grey and brown quartzites, the latter being spheroidal in 

shape, and containing beautiful specimens of Spirifer and Rhynchonella, various 

porphyries, some sandstone, and pebbles of decomposed rock containing mica, which 

might be weathered granite, are characteristic. They are much larger than the 

pebbles occurring in the lower silts and in the modern stream channel. The 

extension of the gravels over the Divide is interesting. The biggest boulder 

observed is found embedded in clay in a cutting right on the main Divide. It is 

porphyry, and is four feet high and two feet across. 

The gravels are found on a variety of local rock types. Around Wallerawang, 

for instance, they are deposited on shale. In the vicinity of Irondale (e.g., at 

the mouth of Thompson's Creek) the local rocks are sandstone and grit. On the 

Main Divide, again, shale is found. It is apparent that the homogeneous gravels 

PIPER'S FLAT DEPOSITS. 

Text-fig. 6. — The Piper's Flat Deposits. 

A line of gravel extends right along Piper's Flat over the Main Divide. 

Consideration of a number of factors shows the possibility of it being river 

gravel. 

could not have been derived from the rocks on Avhich they rest, although every 

rock-type found in them may have come from the district. The conclusion is, 

therefore, that they represent an old stream line about 50 feet above the modern 

flat, and have been put in their present position by stream action. Possibly, in 

time past, they extended over the area now occupied by the lower Piper's Flat. 

An interesting confirmation of this view is obtained from Slaven's Cave, four 

miles up Thompson's Creek. This cave is situated on a hillside in hard porphyry, 

and was probably formed by the dissolving out of a small limestone pocket. Part 

of the roof has fallen in, but the cave is still about thirty yards across, and twenty 

to thirty feet high. A small hole leads into it from the top. The floor, which is 

about sixty feet above the modern stream, is covered with fine brown laminated 

silt, although now no water flows through the cave. Other unexplored caves 

occur below. The floor of the cave represents a higher old stream-level, which 

agrees with the evidence of the gravels. 

 In considering the character of the gravels, other points have to be borne 

in mind. Near Piper's Flat railway station, on Gow's Creek, coarse conglomerates 

are overlain by fine silts. Right along the southern side of the valley the soils 

are fine, with a few small quartzite pebbles. The Upper Marine conglomerates 

between Wallerawang and Rydal weather to a depth of about two feet, giving a 

fine sandy soil. On the other hand, the gravels along Piper's Flat are up to 30 feet 

thick, and are packed together in brown clay, especially in the type beds near 

Irondale. This clay is quite different from the surrounding soil, but might have 

been derived from weathering of granite pebbles. Be that as it may, the fact 

Text-flg. 7. — Liithgow Valley, which was eroded near base-level. 

Note the course of Marangaroo Creek between the two monadnocks, the valley 

levels at 3,000 feet cut in a plateau of average elevation 3,400 feet, the 

entrenched meanders of the streams, and the valley divides of Marangaroo 

Creek. 

remains that no weathered conglomerate in this district is similar to this well- 

defined line of gravel. There seems to be strong evidence, therefore, that these 

are recent stream deposits. 

About two miles to the south-west of Wallerawang the Cox River plunges 

into a gorge, a good view of which is obtained from where the Portland Road 

crosses the stream. This gorge attains a maximum depth of 700 feet to the 

east of Rydal, and ends just above the Lett River, where it emerges from a well- 

defined scarp. Near Hartley the river is but little entrenched in the flat 

Kanimbla Valley. Below Wallerawang the stream is obsequent, a fact which is 

interesting when considering the past stream history. This fact bears no relation- 

ship to the silt flats along Cox's and Piper's Flat Creeks, which could not have 

been laid down along the present slope. Also, there is no silt in the broad valley 

 to the east of Wallerawang, just above where the stream flows into the higher 

land. An account of Solitary Creek is given when the Cox Divides are discussed. 

Lithgow Valley (Text-fig. 7) is found on the same level as Wallerawang Valley, 

and consists of Upper Coal Measure and Upper Marine rocks, and granite. To the 

north rises the Blue Plateau, whilst to the south the old mountain masses of 

Mounts Walker and Flaherty are found. The valley is about 500 feet deep, from 

one to three miles wide, and is drained by Farmer's and Marangaroo Creeks. The 

former shows entrenched meanders along the lower part of its course, where it 

has cut a steep gorge, 500 feet deep, in the valley levels near the Cox junction. 

The divide between this stream and Marangaroo Creek to the west of Bowenfels is 

almost non-existent. The break in the divide is so large that the valley between 

Bowenfels and Marangaroo is continuous. In view of this fact it is all the more 

remarkable to find Marangaroo Creek flowing into the high mountain block (Text- 

fig. 4). The stream is certainly antecedent, and this part of Lithgow Valley is 

the result of differential erosion. The stream originally flowed over a plain of 

Hawkesbury sandstone between the two residuals. After the uplift which resulted 

in the formation of the Lithgow and Wallerawang levels, the stream graded a large 

part of its course, but could do very little lateral cutting near its mouth on 

account of the extreme hardness of the steeply-inclined quartzites. Further 

upstream, however, after cutting through the hard Hawkesbury beds, it discovered 

the softer Upper Coal Measure series below, and excavated a wide valley in them. 

A large relic of the original plateau is preserved on the 3,300 feet level to the 

south-east of the junction with the Cox. The upper and middle courses of 

Marangaroo Creek were determined by the master-joints of the Hawkesbury sand- 

stones (i.e., in north-south, and east-west lines). The lower course was deter- 

mined by the strike — about 20 degrees east of north — of the Devonian quartzites. 

The lower course of the creek shows deeply entrenched meanders, relics of the old 

plateau surface stream. 

The upper course of Farmer's Creek has also been determined by joints. 

The lower course is old, and is mainly in softer granite and slate, avoiding the 

hard quartzites. Owing to the comparatively soft granite along its lower course, 

the stream has, unlike Marangaroo Creek, been able to prolong the upper 

(Lithgow) valley levels right to the Cox, although now it is deeply entrenched 

in them, below Bowenfels. A small plateau at 3,400 feet is found to the east of 

Farmer's Creek. The eastern side is a steep cliff — known as Hassan's Walls — 

which overlooks the Kanimbla Valley. The 3,100 feet level extends within a 

mile of Hartley, which is at 2,400 feet. 

With regard to the idea of benching as the main cause of the valley, as 

suggested by Mr. Sussmilch, I have no doubt that benching is mainly responsible 

for the level valley above Lithgow, but has been only a minor factor in the 

evolution of the remainder of the valley floor. 

Boyd and Budthingeroo Creeks. — The topography of the country around the 

heads of Kanangra River, Boyd and Budthingeroo Creeks is varied. Three series 

of valleys are found at various levels. Of these, the valleys of Kanangra Platform 

(3,300 feet) have already been described. The upper valleys of Boyd and 

Budthingeroo Creeks are at 3,750 and 3,950 feet respectively. They are mature 

in type, being more than one mile wide, and are occupied by sluggish streams 

flowing over swampy flats. On the traverse line they are both found at a depth 

of 300 feet below the plateau, which varies from 3,950 feet to the east of Boyd 

Creek to 4,250 feet between the two streams, attaining a like elevation to the west 

of Budthingeroo Creek. Here the principal rocks are granite and slate, giving a 

heavy clay soil. These valleys are referable to the Lithgow and Wallerawang 

Valley class, and are similar to those at Oberon and Shooter's Hill. 

In this vicinity, along the Tuglow-Kanangra divide, mature relic valleys at an 

elevation of 4,100-4,200 feet are found. These are 200 to 300 feet above the previous 

series, and drop steeply into the latter. These valleys are cut about a hundred 

feet in the soft Silurian rocks of the Jenolan Plateau, resembling the mature 

valleys half-way between Hampton and Jenolan, and the early mature valleys at 

Wentworth Falls and on the Kanangra Platform. Their present extent in this 

district is not great, but they appear to be relics of the Tertiary surface. 

Retreat, Tuglow and Fish Rivers. — The upper valleys of these streams also 

belong to this series (i.e., Lithgow), although they are found at variable altitudes. 

The Retreat River at Porter's Retreat is 600 feet below the plateau, at 3,500 feet. 

The Tuglow flows in a mature valley, 300 feet below the plateau surface, which is 

at 4,100 feet; whilst the Pish River at Oberon flows at 3,500 feet, or 500 feet below 

the plateau. 

These three valleys are cut in highly-inclined Silurian strata and in Devonian 

granites, and are, consequently, not due to any such action as benching, which 

was partly responsible for the formation of Lithgow Valley. They were formed 

under much the same conditions, as regards elevation, as the Wallerawang and 

Lithgow Valleys, are up to two miles wide, each having similar dimensions. One 

is struck by the fact that the Fish River at Oberon, which flows over marshy 

flats, is notably more mature than the same stream at Tarana — and, for that 

matter, Solitary Creek above that point — the latter valleys appearing to be of a 

"masked juvenile" type; that is to say, in point of age the valleys are young, but, 

owing to the softness of the decomposed granite in which they are cut, a stage 

closer to maturity has been reached than would have been the case in the some- 

what harder rocks at Oberon, for example. The grades of Solitary Creek between 

Rydal and Tarana, and the Fish River above Tarana, towards Oberon, are not 

typical of mature streams, being of the average respective orders of fifty and 

forty-five feet to the mile. Below Tarana, the Fish River has an average grade 

of eleven feet per mile into Bathurst. The thalweg of the river is that of a 

rejuvenated stream, supporting the conclusion that the wide valley at Tarana is of 

recent formation, being much younger than the more mature valley at Oberon 

in harder rocks. 

Throughout their lengths, the two branches of the Fish River show well- 

developed meanders, which date back either to the pre-uplift or the Lithgow 

Valley stage, the former being the more probable. The powerful Tuglow has cut 

back into the soft Silurian rocks, the head of erosion now being within three 

miles of the Main Divide. This short length of upland valley is, however, very 

mature. The Retreat River Valley shows a valley-in- valley form, the main valley 

at 3,500 feet being trenched to a depth of a hundred feet at Porter's Retreat. 

Below here, it appears to run into deeper gorges. The occurrence of a zone 

containing these mature valleys entrenched from three to six hundred feet in the 

plateau surface is very interesting. Similar valleys are found on the Middle 

Wollondilly and the Cookbundoon Rivers, as I hope to show in a subsequent paper, 

but do not occur over the main mass of the Blue Plateau, although they are found 

along the Wallerawang to Mudgee railway. These facts are of significance when 

considering the folding and warping movements which the area has undergone. 

Text-fig. 8. — Meg-along Valley. 

Note the broad, flat floor of the valley, the great meanders of the Cox, now 

entrenched m the main valley floor, and the remarkably uniform increase in 

the depth of entrenchment of the streams from north to south. The undissected 

valley floor extends ten miles further northward to Hartley. 

226. PHYSIOGRAPHY OF THE COX RIVER BASIN, 

Kanimbla and Megalong Valleys. — Looking south from Mt. Walker, near 

Lithgow, a splendid view is obtained across the floor of the great Kanimbla Valley 

to Mt. Mouin, twenty-five miles away. Here, three cycles of erosion are clearly 

presented, which have resulted in the formation of the plateau (first level), the 

level Kanimbla Valley (second level), and the Cox gorges respectively. There is 

very clear evidence that Kanimbla Valley was formed not far above base-level. 

The northern part of the valley is clearly separated from the Wallerawang 

levels, the respective average elevations being 2,200 and 3,100 feet. This is 

especially the case near Hartley, where the two — Kanimbla being here at 2,400 

feet — are a little over a mile apart. 

Kanimbla Valley — the southern part of which is called Megalong — extends 

from Hartley in the north to Mt. Mouin in the south, and from the northern cliff 

ramparts near Blackheath to Lowther. It has a length of twenty-five miles, a 

width of ten miles, and a depth of 1,100 to 1,500 feet. To the east of the Cox the 

valley is gently undulating; but on the western side, the valley ridges rise 

uniformly to the Main Divide in the vicinity of Hampton at 3,800 feet. As I have 

already pointed out (under the heading "Blue and Jenolan Plateau") there is 

very good evidence that the western side of the valley has been subjected to 

warping. It might be added that the uniform rise of these southern valley ridges 

— some of which are granite, and others Devonian rocks, both showing long out- 

liers of Upper Marine rocks in parts — from the Kanimbla levels to the Divide is, 

of itself, good evidence of such warping. 

The valley is thus distinctly asymmetric, but the flat northern side varies in 

elevation from 1,900 feet on Megalong and Blackheath Creeks to 2,600 feet 

between Galong and Breakfast Creeks, the average being about 2,200 feet. 

The characteristic features of the valley are shown by a study of the eastern 

end, Megalong (see Contour Map, Text-fig. 8 and Plate xix, fig. 2). The northern 

and eastern confines of this valley are formed by great ramparts of Triassic 

sandstone, from which the softer talus rocks slope away at 18 to 20 degrees into 

a level valley. This valley is occupied by four main streams. Breakfast, Galong, 

Megalong and Pulpit Hill Creeks. The lower courses of the two former streams 

have cut great gorges in the valley fioor, whose deepest parts are only 700 feet 

above the sea. They alone of the northern Kanimbla streams make accordant 

junctions with the Cox. Megalong and Pulpit Hill Creeks have their whole courses 

along the level valley, and make highly discordant junctions with the Cox. The 

former stream plunges down five hundred feet within a few hundred yards into 

the river. 

The canyon which the river has cut in the relatively level valley deepens 

rapidly downstream. At the jun*tion of Megalong Creek, this gorge is 800 feet 

deep; whereas, a little below Galong Creek, it has attained a depth of 1900 feet, 

the great change being due to a rapidly falling stream and a rising upper valley. 

A feature of the valley is the fringe of benches of Upper Marine sandstone and 

conglomerate on the northern and eastern sides. Much of this bench is bounded, 

on the outer side, by cliffs and small precipices up to eighty feet high. The main 

interest of the Megalong Valley lies in the series of valleys found between 1,900 

and 2,300 feet (see Contour Map). 

The early mature valleys at the head of Breakfast Creek and in Megalong 

Gap are of this series, at 2,200 feet; and occur in sandstone and conglomerate. 

The upper valleys of Galong Creek at 1,900 feet occur in granite, 400 feet below 

the conglomerate. Between the two streams, the eastward dip of the conglomerate 

is of the order of a hundred feet to the mile over* a range of two miles; whilst, 

from north to south it is laid down on an undulating granite surface. Megalong 

and Pulpit Hill Creeks flow partly over Upper Marine rocks and partly over 

granite. There is little change in topography in the passage from one series to 

the other, and no noticeable change in stream grade. From this it is to he inferred, 

that differential erosion has not played a great part in the formation of the valley 

floor. 

There are fairly extensive silt flats along Megalong and Pulpit Hill Creeks, 

consisting of flat, badly-drained silts, up to four hundred yards wide, and of some 

depth. These are mainly of sand; Plate xix, fig. 2, gives a typical view. These 

flats extend right up to the steep talus slopes, and appear to be swamp or lake 

deposits. They contain no stones. Obviously, these flats could not have been 

formed under existing conditions, as the streams ara just trenching them and 

washing away the earth. They must have been deposited along the level valley 

floor before the lowest courses of the streams had their pi'esent grade, that is, 

before the Cox cut its deep modern gorge in the valley floor, at a time when this 

valley floor was near base-level. 

It appears highly probable that the warping of western Kanimbla affected the 

valley to the east of the Cox, as the edges of these eastern ridges adjacent to the 

river are somewhat higher than the land a little further to the east in the valley. 

This is also the case with Blackheath Creek. Such warping, whether near, or a 

good deal above base-level before the cutting of the modern gorges, would cause 

the creeks to slow down, depositing part of their loads of rock waste to form these 

flats which are, of course, rather temporary features. 

The topography of the remainder of Eastern Kanimbla is very similar to 

that of Megalong Valley, being, possibly, a little more subdued on account of the 

greater predominance of granite. The silt flats of Blackheath Creek at 2,000 feet 

are very extensive, whilst the valley of Lett River is very flat. 

When we turn to consider the modern course of the Cox, we are struck at 

once by the variations in the amount of dissection going from north to south. 

Near Hartley, the river is entrenched only a couple of hundred feet in the level 

plain. At Megalong Creek the depth of entrenchment is 800 feet; whilst for 

twenty miles below Galong Creek the canyon of the Cox is nowhere less than 

1,900 feet deep. Turning to the tributaries, the variations are still more striking. 

Lett River, Blackheath, Pulpit Hill and Megalong Creeks make discordant — in 

the latter cases highly discordant — junctions with the river. Turning to the 

western side, Kanangra and Jenolan Rivers make strictly accordant junctions 

with the Cox. Little River and Gibraltar Creek are not strictly accordant, whilst 

the junctions of the other streams, Cullenbenbong, Long Swamp and Lowther 

Creeks, for example, are discordant. The character of the gorge is clearly shown 

by Text-fig. 1. The effective head of erosion for the tributaries is now at the 

junction of Megalong Creek, although the Cox itself has cut back further. From 

these considerations, two definite conclusions can be drawn: firstly, Kanimbla 

Valley is mature, and a fairly ancient feature; secondly, the modern gorges of 

the Cox and its southern tributaries have been formed recently. In other words, 

this valley fioor has only recently been raised far above base-level. Summing up, 

the Kanimbla Valley represents a stage, rhythm, or pause in the uplift of the 

plateau, of fairly long duration. 

The Relationship hetween the Kanimbla and Walleraicang Levels. — The change 

from the Kanimbla to the Wallerawang levels — from Hartley to South Bowenfels 

— is marked by a great change in stream-valley topography. At Hartley, the Cox 

is liitle entrenched. Going up the river, however, a deep gorge is entered, which 

extends almost to Wallerawang, attaining a maximum depth of 600 feet near 

Farmer's Creek. The lower parts of Farmer's and Marangaroo Creeks have also 

cut deep canyons in, or, in the latter case, below the 3,100 feet level. These gorges 

extend some three miles up the streams, and are only just beginning to attack 

the soft upper valley levels. Of the twenty-four miles of river line between 

Narrow Neck 

Text-flg. 9. — The warped valley of the Kowmung River, 

(a) shows the rising warp as viewed from Mt. Mouin. (ft) gives a view loolting- 

to the south from Mt. Solitary. In each case the warped valley floor is seen to 

be little dissected. (c) shows the old valley floor looking northwards from 

Bindook Swamp. Note the striking "valley-in-valley" structure, and the fault 

scarp to the west (left). 

Hartley and the head of the Cox, only the lower thirteen miles are characterized 

by gorges. The junctions of these two streams with the Cox are accordant, in 

strong contrast to the discordant junctions of the tributary streams in the softer 

rocks below Hartley. The limited extent of the gorges, the steep grade of the 

river — forty feet per mile — and the fact that Solitary Creek runs 500 feet above 

the Cox, and is separated from it by an insignificant valley divide, are certain 

evidence that the gorges have been recently cut, with a lower limit of 2,200 feet 

(Hartley). That is, the Kanimbla levels have acted as a temporary base-level 

BY F. A. CEAFT. 

229 

of erosion for the Wallerawang levels. The physiographic fault between the two 

is evidence of the same thing (see Text-fig. 12). 

The dissection of the higher levels has only been made possible recently by 

their uplift above the Kanimbla levels. That is, both the Wallerawang and 

Kanimbla Valley systems were formed at a constant level, and were co-extensive. 

Thus the upper valley once extended without a break from Piper's Flat and 

Wolgan Gap to Mt. Mouin. The consequences of this conclusion are fully 

discussed when the folding movements are considered. 

Jamieson's Valley and the Kowmnng Basin. — -The lowlands of Jamieson's 

Valley are separated from the Kanimbla levels by a uniformly sloping surface, 

which has not been much dissected apart from the canyons of the Cox and 

Kowmung Rivers. The steady slope from Jamieson's Creek to Gangerang Range 

on the south, and Mt. Mouin on the north of the Cox, is a very striking feature. 

The Cox and Kowmung Rivers have cut extremely deep and narrow gorges in 

this surface, which vary in depth from zero at Black Hollow Creek to 2,000 feet 

between Mt. Mouin and Gangerang. The smaller streams flowing from the foot 

of Mt. Mouin are but little entrenched in this surface, although, as we have seen, 

the more powerful streams a little further up the Cox Valley, such as Breakfast 

and Kanangra Creeks, are flowing in very deep gorges similar to that of the 

Kowmung. 

"KTT .1800'. 

Text-fig-. 10. — Lower Jamieson's Valley, showing the antecedent course of 

Jamieson's Creek and the stream flats due to the rise of the warp to the south- 

west. The w^arp surface is very little dissected, and rises steadily towards the 

south and south-west. Cedar Creek (near the western margin) is a subsequent 

stream. (Drawn from Contour Map.) 

Jamieson's Valley is bounded on three sides by precipitous cliffs of Triassic 

sandstone, the open southern margin shading almost imperceptibly into the 

Kowmung Basin. But for the fact that the Cox River cuts across here, it would 

be impossible to distinguish between the two features. On the north-east, the 

plateau rises 2,300 feet above the valley floor, but on the south-western margin, 

the elevation above the tilted western margin is only about 1,000 feet (Text-fig. 9). 

There are extensive silt flats along the middle portion of Jamieson's Creek 

in the vicinity of 500 feet (see Text-fig. 10) similar in many respects to those of 

230 PHYSIOGRAPHY OF THE COX RIVER BASIN, 

Megalong. Along Reedy Creek especially, islands rise from these flats like islands 

from the sea. The flats themselves are absolutely level, and consist of fine sands 

and clays. There are no large stones in these silts, and very few small ones. 

Doubtless there were some in the original deposit, but owing to the subsequent 

action of air and water over a fairly lengthy period, they have been disintegrated. 

I am strongly of the opinion that these flats are due to the deposition of 

silt in a body of water. They are not due to the occupation of the valley by 

swamps, as peat is not found in them. Sword grass and rushes are absent, and 

gum trees and grass grow right to the creek. For all that, the heads of the 

flats are, as yet, badly drained, and are submerged in wet weather to a depth of 

several inches. 

The origin of these flats is fairly obvious. The streams had cut down almost 

to base-level along their lower courses, forming a flat-bottomed valley. The edge 

of a warp has risen across the lower three miles of Jamieson's Creek, which was 

not able to keep pace in downcutting with the rise of the warp. The stream 

was, therefore, partially dammed, causing the formation of a lake on the upstream 

side, in which silt was deposited. This lake acted as a temporary base level of 

erosion for the Jamieson's Creek basin, and, in course of time, became almost 

silted up. 

At the mouth of the creek, the warped surface has reached a height of 775 

feet above sea-level, 275 feet above the silt flats at 500 feet. Thus the creek is 

antecedent. On the southern side of the Cox, at the head of the Kowmung River, 

the warped valley surface has attained an elevation of 2,800 feet. The lower part 

of Jamieson's Creek, which has a meandering course, is entrenched some 300 feet 

in the surface, and flows in a steep gorge cut in hard conglomerate. Headward 

erosion is just beginning to affect the lower margin of the flats, which have been 

trenched to a depth of twenty feet. The upper portion is, as yet, practically 

unaffected, although some terracing of the order of five feet, is shown at the 

junction of Reedy and Jamieson's Creeks. 

The conditions of deposition appear to have been very similar to those which 

prevailed on the Nepean River during the deposition of the silt lakes at Wallacia 

and elsewhere, the general characteristics of the two deposits showing a marked 

similarity as regards material and stratification. 

The other stream of Jamieson's Valley does not show these features, being a 

revived ancient stream at present having a consequent character, and is uniformly 

entrenched in the warped plain. In general, Jamieson's and Megalong-Kanimbla 

Valleys are closely related from a physiographic point of view. 

The Koiomung Basin. — The topography of the Kowmung Basin is comparatively 

simple. In brief, the area consists of a ramp (Figs. 1, 9), which rises from 300 

feet in the north-eastern corner to 2,800 feet in the south, at Bindook Swamp, and 

3,000 feet near Kanangra Walls to the west. It is bounded on the east by the 

Tonalli Range, which varies in height above the ramp from 1,600 feet in the north 

to 300 feet in the extreme south, on the Wollondilly divide, the actual respective 

elevations of the range being 1,900 and 3,100 feet above the sea. The western 

edge consists of a scarp — partly valley wall, partly fault scarp — whose height 

above the ramp varies from 1,600 feet at Gangerang to 800 feet in the vicinity 

of Mt. Shivering. This surface has a remarkably uniform upward slope from the 

north to the south, Kiaramba Ridge, to the east of the Kowmung, being typical 

(Text-fig. 12(7). 

BY F. A. CRAFT. 231 

Its surface consists of Silurian, Devonian and Upper Marine rocks, and must, 

therefore, be a surface or plane of erosion. The streams have trenched this 

surface with profound juvenile gorges, up to 2,000 feet deep, but the upland form 

is but little altered, mature valleys being preserved right on Kiaramba Ridge. 

The main features of warping and past stream history are discussed under 

separate headings. 

Jamieson's Valley and the Kowmung Basin form a great oval-shaped valley 

which opens in a general way into the Wollondilly Basin to the south. The outlet 

of the Cox is hardly noticeable in the eastern wall of this valley, being only a 

mile and a half wide at the top. Byrne's Gap, at the head of the Tonalli River, 

which is not occupied by any stream, is almost as wide. The true beginning of 

the "bottle-neck" constriction of the Lower Cox-Warragamba is not below the 

Wollondilly junction, but below the King's Tableland-Tonalli Range scarp. 

At present, the 300 feet level is the base-level of erosion for the Kanimbla 

Valley. This latter surface continues t-o the east of Megalong Gap and Mt. Mouin, 

sloping thence uniformly, as an almost unbroken surface into Jamieson's Valley. 

Valleys of the Loioer Cox-Wollondilly. — The valleys of the Lower Cox and 

Wollondilly are excavated in the steps and slopes leading up to the main plateau. 

Here the streams have a low grade and run in deep valleys, whose depth varies 

from 2,000 feet in Upper Burragorang, and 1,700 feet in Lower Burragorang and 

the Lower Cox Valley, to 1,400 feet at the junction of the Cox and Wollondilly. 

The lower thirty miles of the valley of the Wollondilly are known as 

"Burragorang". An idea of the general appearance of these valleys is gained 

from Text-fig. 1 and Plate xx, fig. 2. 

The Lower Cox-Wollondilly system comprises five valleys — namely Burra- 

gorang, the lower valleys of the Cox and Nattai Rivers, and those of Green Wattle 

and Lacy's Creeks. The average width of the Burragorang between cliff lines is 

somewhat less than two miles (contrast with the eight-mile-wide main Kowmung 

Valley). That of the Lower Cox is up to a mile and a half wide; whilst the other 

three vary from half to three-quarters of a mile in width. The floors of the two 

main valleys are flat, and consist of rich alluvial deposits up to half a mile wide, 

which the rivers are trenching. A typical section at the junction of the two rivers 

is shown in Text-fig. 11, and shows small water-worn pebbles and peat under- 

lying horizontally-bedded silts consisting of alternate layers of roots and plant 

remains, and plain silt, with thin layers of peaty material. The alluvials extend 

up the Cox above Pearce's Creek, and up the Wollondilly above Byrne's Creek. 

Terracing is very noticeable at the junction of the two rivers, three terraces being 

found at 180, 200 and 240 feet, the second being the most important. The last- 

named is met with on Pearce's Creek on the Cox, and also above Fitzpatrick's 

Crossing on the Wollondilly, three miles above the Cox junction. Further up the 

Wollondilly, higher terraces are met with. At the mouth of Byrne's Creek, twenty 

miles above the Cox, a level detritus and silt plain occurs at 420 feet. A certain 

amount of uplift towards the south is very probable. The silts extend about a mile 

down the Warragamba, the lowest reliable level being at 150 feet above the sea, 

below Gogongolly Creek. The thickness of the deposits in any one place cannot 

be exactly determined, but the maximum is probably of the order of fifty feet at 

the Cox-Wollondilly junction (this is the 200 feet terrace). 

These silts appear to be very similar to the silt lakes found on the Nepean at 

Wallacia, Penrith and Camden, and appear to have had a similar origin. In this 

case, a rising warp across the Warragamba caused the formation of a lake, as the 

232 

PHYSIOGRAPHY OF THE COX RIVER BASIN, 

stream was not able to cut down as rapidly as the barrier was elevated. Pauses 

in the uplift are indicated by the formation of the root beds, when the river was 

able to cut down and partly drain the lake. A period of standstill is now allowing 

the streams to cut down and erode the deposits. 

These valleys are enclosed by rampart-like cliffs of Hawkesbury sandstone, 

which form almost unbroken walls. Two particularly fine lengths occur, the 

"Burragorang Walls" and the Walls of Green Wattle Creek. The former are on 

the eastern side of the Wollondilly above the Nattai junction, whilst the latter 

Firsr Terrace. eod) 

SeconlTer r a.ce(£.ifr«5) 

Of-hers. (35o'-t.oo'). 

Modern Gravels, 

Scale ? " JM 

Text-fig. 11. — Silts and Terraces of the Lower Cox- Wollondilly. 

The section proves the nature of these silts, showing that they are old lake 

deposits. The peat and root beds are particularly notable. Rising terraces 

further to the south indicate uplift in that part. are about five miles above the Cox junction 

with that stream, and also have a westward aspect. 

In both cases, the cliffs are quite straight, and almost unbroken, and are not even notched by tributaries. 

Thus they are quite different from the cliffs of the Grose and Jamieson Valleys, which are deeply cut into, 

even where mere wet-weather streams cross them. This absence of tributaries seems to 

indicate a recent formation for these streams, a conclusion supported by absence 

of meanders, whilst the straight and unbroken character of the cliff lines would 

appear to indicate a recent date for the excavation of the valleys themselves, 

a conclusion, as we shall see, in line with other evidence. 

The course of Green Wattle Creek is interesting. Seven miles from the Cox 

the valley is almost a mile wide, the eastern edge being the straight walls just 

mentioned (Plate xx, fig. 1). The floor at 400 feet consists of sandy silts with 

layers of water-worn pebbles and of peaty material. The creek is slow and wide, 

running in a sandy channel. A mile below this point, the stream runs into a rocky 

gorge, cut in a terrace of hard Permian sandstone, which is fairly extensive at 600 

feet. On the stream level between three and four hundred feet, there are flat 

terraces up to a quarter of a mile broad, and to half a mile long, mainly on the 

western side at the mouth of tributary gullies. These alternate with stretches of 

rocky gorge cut in grey tuffs. The last mile is across the Cox Valley flats to the 

river, with which the creek makes an accordant junction, after wandering over 

the flats. The river has apparently dragged the mouth of the creek downstream. 

A feature of the plateau surface in this part is the occurrence of lines of 

sandstone residuals, or rock hills, about two hundred feet high. One line is found 

along the King's Tableland; others between Black Hollow, Green "Wattle, Lacy's 

Creeks and the Wollondilly River; and another very fine line between the Wollon- 

dilly and the Nattai (Plate xx, fig. 2). In some cases, these residuals occur right 

on top of the modern cliffs, and appear to have extended at one time into the area 

now occupied by the valleys. They are hemi-spheroidal to conical in shape, cut 

out of sandstone of uniform hardness, and are most likely old basalt caps or 

residuals from which the basalt has been removed. These lines are parallel to 

the Mt. Tomah-Mt. Wilson residuals. No other explanation is apparent. The 

residuals indicate that the older valleys (pre-uplift) in this part were a good 

deal narrower than the modern ones. The fact that all these valleys are of the 

same order of magnitude is important when considering the evolution of the 

stream system. 

The Warragamba Gorge. — This is, perhaps, the most remarkable of all the 

Cox-Wollondilly canyons, not as regards depth, for its maximum depth, 1,600 feet, 

is only half that of Kanangra Creek Canyon, but on account of its extreme 

straightness. Of a course of fourteen miles between the Wollondilly-Cox junction 

and the Nepean, nine miles are almost perfectly straight, even the ends of the 

gorge being only slightly bent. Thus this stream is eminently young, and 

contrasts strongly with the upper and middle sections of the Cox which flow 

in great meanders. 

For the greater part of its length the sides of the gorge are almost precipitous, 

the river occupying the whole width of the bottom of the gorge. Above "The 

Bend", three miles below the Wollondilly, the gorge widens notably, as the soft 

Upper Coal Measure shales, rising gradually towards the west, are exposed to the 

attack of the stream, which has cut terraces or benches at high flood level. The 

entrance from Burragorang (Taylor's "Warragamba slot") is considerably wider 

than a view from that valley would appear to indicate. It is actually a narrowing 

continuation of the Lower Cox or the Lower Burragorang Valley. 

Going downstream into a narrowing canyon, sandbanks and terraces are met 

with until five miles below the Wollondilly. As the cliffs close in on the river, great 

boulders are found in the river bed, and on the hillsides up to high flood level, sixty 

to seventy feet above the stream. Coming to Monkey Creek the gorge, now sixteen 

hundred feet deep, has narrowed into a ravine. Immense boulders up to twenty 

feet long, fifteen feet high and ten feet wide are found by the side of the river, 

whose channel is, however, fairly clear. The cliffs come down steeply almost to 

the water's edge. Towards the lower end, within two miles of the Nepean, another 

change is noticed. The banks of the river are almost perpendicular, and the zone 

of scrub, till now so conspicuous a feature within the flood limits, is absent. This 

is the steepest-sided part of the canyon, although it is only three to six hundred 

feet deep. At the junction with the Nepean, near Wallacia, shingle beds are met 

with. Within the Warragamba gorge, the shingle beds extend only three miles 

below the Wollondilly — an indication of the swiftness of the flood waters in this 

narrow track, although the average grade of the river is only seven feet per mile. 

The zone of scrub on either bank of the river is a most remarkable feature. 

There are no trees within the flood limit, but scrub, with little undergrowth, is 

found, with the characteristic downstream bend. Above this zone rise the forest 

trees, grey gum and turpentine. The scrub zone is littered with boulders and 

flood debris, and is almost impassable. The bottom of the gorge thus has the 

appearance of a lane — the river — running between footpaths which are, in turn, 

bordered by hedges, forest trees and cliffs. 

The sides of the main gorge are indented by tributary gullies, all of which 

are discordant, coming in a little below high flood level. As these creeks only 

run in wet weather, they could hardly be expected to cut down to the normal 

low river level. Uplift had also something to do with the arrangement, as tiny 

wet-weather streams could not keep pace in downcutting with the main stream. 

The position of the uplift which caused the formation of the Cox-Wollondilly silt 

lakes is of some importance. An uplift of the order of three to five hundred 

feet at Wallacia partly blocked the Nepean in a similar manner. As this uplift 

is across the Warragamba also, and took place very recently, as is indicated later 

in this paper, it could readily have caused the partial blocking of the Warragamba 

also, and the formation of silt lakes at the head of the canyon. Recent faulting 

has also taken place across Monkey Creek, according to Willan. 

The significance of the newly-formed Warragamba with regard to the 

question of past stream fiow will be discussed later. 

Main Folds and Warps of the Area. 

The folding and warping movements which have affected the regions adjacent 

to the Sydney Basin have been noted by Andrews (1903) and described fully by 

Taylor (1923). Other contributions to the subject include Professor David's 

papers on the Monocline (1896) and the Kurrajong Fault (1902), and papers by 

Taylor, more specifically his contribution to the Pan-Pacific Guide Book (1923) ; 

Willan's "Geological Map of the Sydney Basin" (1925) is also very valuable for 

the area which it covers. It will be seen that the main Blue Plateau has scarcely 

been touched. 

Surrounding the Sydney Basin, which is a neutral or "stillstand" area, there 

are three main lines of warping — the northern or Hawkesbury Warp, including 

the country between North Sydney and Broken Bay; the Blue (Mt.) Monocline 

fold and warp system, which extends from the north of Kurrajong, southwards 

to Mittagong; and the Southern Warp, or Nepean Ramp, which, beginning at 

Cook's River (Sydney), merges into the southern highlands in the vicinity of 

Moss Vale. This much is proved, but the actual uplift of the main mass of the 

Blue Plateau has, as yet, been a subject of conjecture. In this account, I propose 

to treat the Cox Basin specifically, making some reference to relevant adjacent 

areas. 

General Considerations of the Folding. — In making a general survey of the 

country between the Hunter River basin and Lake George, one is struck by the 

regular variations of altitude. This is particularly the case near the coast, where 

the Sydney Basin lies between two high areas of warped country. Further to the 

west, in the region with which this paper deals, variations of altitude are notice- 

able, which can be correlated, in part, with the littoral features. 

The dominant movement of uplift in tlie eastern portion of New Soutli Wales 

has been extended along north-south lines. If it is thought that uplift took place 

simultaneously along the whole line, variations of altitude from place to place 

would be due to simple differential uplift; if the view is taken that these high- 

lands have been built up by a system of rather localized uplifts, warp and fold 

lines with an east-west trend would be found, marking the northern and southern 

limits of each movement of uplift. Such lines of warping are found to the north 

and south of the Sydney Basin, and continue, as will be shown in the latter case, 

to the west. 

The eastern Highlands of this State fall into three groups — the New England 

Plateau, rising to 5,500 feet; the Central, or Blue, Plateau, with a maximum 

elevation of 4,400 feet; and the Southern Highlands, extending from the Federal 

Capital Territory to Kosciusko, which have peaks over a wide area from 5,500 to 

7,200 feet above the sea. The northern and central sections are separated by the 

Cassilis Geocol, at 2,000 feet; and the central and southern massifs by the Lake 

George geocol, at 2,100 to 2,300 feet. The Central is the most limited of the 

plateau massifs. A good deal of its elevation appears to be due to the over- 

lapping of the main northern and southern uplifts in that section. 

In dealing with the uplift of this central area included in the Cox region, 

the more recent earth movements have been described and located first, and the 

earlier folding movements identified by a process of elimination. 

The Mulgoa Step. — The section of the eastern face of the monoclinal fold 

extending from Kurrajong Heights to Douglas Park is the result of very recent 

uplift. This is clearly shown by the silts of the Lower Cox-Wollondilly. Obviously 

the silts are of more recent age than the valleys in which they are found, these 

valleys, in turn, being younger than the uplift which led to their formation. 

The uplift responsible for the partial blocking of the Warragamba was younger 

than the Lower Cox-Wollondilly Valleys, and, consequently, much younger than 

the uplift which led to the formation of those valleys. This same uplift led to 

the blocking of the Nepean above Wallacia. 

It is suggested that this last phase of uplift only affected the country for a 

limited distance behind the modern monoclinal face, over a maximum width of 

six miles, but generally less than that, and was responsible for these features: — 

(1). Most of the uplift and faulting at Kurrajong Heights, which extends 

to the south across the Grose River, and across Blue Gum Creek, to the north of 

Springwood. 

(ii). The anticline at Glenbrook, with a fault on its western side to the 

south-east of Glenbrook station. 

(iii). Uplift at the junction of the Warragamba and Nepean Rivers, together 

with folding and faulting at Bent's Basin, faulting across Monkey Creek and at 

Razorback Range. Most of these features are clearly shown on Willan's map. 

Additional proof of the recency of this uplift is given by the undissected 

nature of this eastern edge; even the soft shales of Kurrajong, lying on a steep 

slope, are practically undissected. At Mulgoa, the uplifted step to the east of 

the Nepean, which has undergone a general uplift of 500 feet, rising to 800 at 

one point, has been but little attacked by streams. To the east of The Oaks, the 

soft shale slopes have not been cut into much by Mt. Hunter Rivulet, but the 

later uplift here has only affected the country for about three miles to the west 

of the monoclinal face. Razorback Range, also very little cut into, may have been 

affected by this recent uplift. 

The undissected character of this edge is in striking contrast to the amount 

of dissection which the streams immediately to the west have accomplished. 

Blue Gum Creek, to the south of the Grose is, for instance, perched on the top of 

the fold. A few miles to the west, Linden and Wentworth Creeks have trenched 

the plateau deeply right to their heads. 

The western side of the Glenbrook anticline is also undissected. The river 

gravels scattered over the surface of Lapstone Hill, and also on the hilltops of 

Wallacia, are recent deposits. These loosely-cemented, or uncemented deposits 

cannot remain long on the hillsides, as they disintegrate rapidly, and are washed 

away. They cannot be compared, in point of age, with the Kanimbla Valley, or 

even with the lower valleys of the Cox and Wollondilly. This is significant, as no 

notable stream change has taken place since these gravels were elevated, which 

was, comparatively, very recently. 

Jsleioer Uplifts. — The Kotvmung Warp.— Between the Hunter River Valley 

and Lake George, the age of uplift of the plateau varies regularly from north 

to south. The Colo River and its tributaries have cut great canyons in the hard 

Hawkesbury Series, right to their heads. The great mass of the Southern 

Plateau in the districts of Taralga, Moss Vale, Goulburn and the Upper Shoalhaven, 

is very little dissected. At Tallong, for instance, the uplands are flat and swampy, 

only two miles from the Shoalhaven gorge; and there are large areas of mature 

valleys in the Upper Wollondilly and Abercrombie basins which have no counter- 

part in the Grose and Colo systems. The Cox represents an intermediate stage, 

where the eastern section is deeply dissected, but the western part has suffered 

little dissection. 

The idea that the southern part of these highlands has been, in general, 

uplifted at a more recent time than the northern part, receives striking confirma- 

tion when a detailed examination of the topography and physiography is made. 

I have applied the name "Kowmung Warp" to the warping movement which 

is typified by the tilted plain of the main Kowmung Valley between the Cox River 

and the Kowmung-Wollondilly divide between Mts. Colong and Shivering. The 

characteristics of this surface are shown clearly in Text-fig. 9. 

Two lines of evidence — geological and physiographic — go to prove that the 

whole surface comprised in the valley floor which stretches from Mt. Solitary 

in the north to the Kowmung-Wollondilly divide in the south is a warped surface. 

The Kowmung Valley, part only of which is occupied by the Kowmung River 

system, rises southwards in a gentle, almost unbroken, slope. To the west of 

Jamieson's Creek, a similar ramp leads up to the Kanimbla levels near Mt. 

Mouin, and the Gangerang Range. These slopes, which are very even, are 

trenched by the great gorges of the Cox and Kowmung, but these gorges occupy 

a relatively small part of the valley floor. This ramp, or upper valley surface, 

could not have been cut at its present elevation above base-level. It is clearly 

an old plane, or surface of erosion, which has recently been uplifted and trenched 

by juvenile canyons. That this uplift is recent is shown by the fact that streams 

rising near the base of Mt. Mouin, and flowing south and east to the Cox, have 

not cut down much, and are merely nibbling away the edges of the Cox gorge. 

The more powerful streams, such as the Cox and Kowmung Rivers, Cedar Creek 

and, to the west. Breakfast and Kanangra Creeks, have graded their channels, 

but still flow in extremely narrow gorges. Black Hollow Creek is not much 

entrenched in the surface, and the shale beds leading down from Kiaramba Ridge 

to the Cox near Black Hollow Creek are almost undissected. 

The evidence offered by Jamieson's Creek very definitely confirms this idea 

of warping, and is of the utmost value as a positive proof of the nature and 

recency of the warping. The relationship of the valleys to the tilted plain is 

clearly shown in Text-fig. 12. Thus Kanimbla-Megalong Valley bears the same 

relationship to Jamieson's Valley as the Wallerawang levels bear to the Kanimbla. 

In either case a flexure separates the valleys. The other evidence in the matter 

is more geological in character. 

PorMana 

Mam 

Divide Wallerawang r, 

A 

Hartley -^ 

ue Plai-e.aa35 Q0_jg^ , K &l-oombd Kowmung 

■S.&E. Divides of Kowmung 

W Scarp of Ton a II I Ra 

Text-fig. 12. — The Relationship between the Plateaux and Valleys of the Area. 

(A) shows the parallelism of the valley levels of the Cox with the plateau 

surface. Comparison is possible by projecting the two section lines of unequal 

lengths (broken lines) on to a straight line of uniform direction, thus giving 

the components of the various slopes, and hence the amount of folding in the 

given direction. (B) shows the two flexures in the foriner co-extensive valley 

levels, and their influence on the grade of the Cox River. (C) illustrates the 

effect of the Kowmung Warp on the plateau and the valley floor, and the rise 

up to the high Jenolan Plateau from the Blue Plateau level. Graph (i) is 

perpendicular to (ii) and (iii), and intersects them at Bindook Swamp. These 

figures constitute a deductive proof of the folding theories of this paiier. 

The deformation due to late warping is clearly shown by the Upper Marine 

sandstones between Jamieson's Creek and Mt. Mouin. These beds rise at the 

rate of 280 feet to the mile into Megalpng Gap, and present an almost unbroken 

surface, very similar to that of the Hawkesbury sandstones of the Blue Plateau. 

An area of relative depression exists between the foot of the Mt. Solitary talus and 

Mt. Mouin (Text-fig. 9B) to the south-west. Here there is a marked change in the 

slope of the sandstone. To the east, and under Mt. Solitary, the beds are sub- 

horizontal; to the west, they rise at the rate of 2S0 feet per mile — a slope far 

greater than that of the corresponding part of the Blue Plateau between Went- 

worth Falls and the Marked Tree (beyond Katoomba) which is of the order of 

130 feet per mile, or the 170 feet to the mile rise of the Upper Coal Measures 

between Woodford and Katoomba. These, it may be noted, are maximum slopes. 

To the north of Megalong Gap, the series is sub-horizontal to Hartley, to the 

north of which there is a step up of the order of 500 feet to the Lithgow- 

Wallerawang levels. Cedar Creek, to the south-west of Mt. Solitary, flows along 

the north-eastern margin of the steep slope leading up to Mt. Mouin and its 

slight, uniform gradient in a gorge up to 600 feet deep, distinguishes it from 

Jamieson's Creek, the mouth of which only has been affected by the warping 

(Text-fig. 12A). 

It is highly probable that the bedding planes of the sandstones are not 

parallel to the general warped surface, since the thickness of the beds varies 

considerably within small areas, the warped surface of erosion in such parts 

apparently cutting across the bedding planes. This variation is well marked 

to the west of Jamieson's Creek. At the junction of this stream with the Cox, 

the Upper Marine beds have a thickness of 300-400 feet. Below Cedar Creek, the 

river flows through a breached anticline of intensely hard metamorphic Devonian 

rock which here outcrops on the warped slope on either side of the river, being 

obscured to the east and west, away from the stream, by the newer sandstone. 

Still further up the river, the sandstones form a capping, up to 200 feet thick, on 

the highly-inclined Devonian beds. A notable thickening to a maximum of 450 

feet is observed in the neighbourhood of Megalong Gap and Mt. Mouin. Three 

miles north of the Gap, on the same level, granite is exposed on the valley floor, 

capped in places with a thin layer of sandstone and conglomerate. Again, erosion 

appears to have taken place across the bedding planes. 

These Upper Marine beds are found right along Kiaramba Ridge, on the 

eastern side of the Kowmung River, and outcrop near Mt. Colong, on part of the 

Kowmung-Wollondilly divide. Towards the head of the main Kowmung Valley, 

highly-inclined Silurian rocks, which contain the Colong Caves, outcrop on the 

upper valley floor, and their bevelled edges form part of the general warp slope. 

Other ridges on the western side of the Kowmung — Gingra, for instance, which 

leads down from Kanangra Walls — are level benches, part of this valley being 

cut in tilted Devonian strata. Near the junction of the Kowmung and Cox, the 

tilted surface is prominent on both sides of the Kowmung. 

This main valley, eight miles wide, is hardly scarred by Black Hollow Creek, 

but the great canyon of the Kowmung is prominent. After passing the gap in 

the Cox divide near the end of Kiaramba Ridge, which is only 800 feet above the 

Cox, the river pursues an antecedent course, flowing into the highlands, and 

joining the Cox in an upstream direction in a gorge 2,000 feet deep. The gradual 

slope down to the Cox on the east of this part of the Kowmung Valley is unbroken 

by large gullies, although it consists largely of soft shales. There are also relics 

of mature valleys on the Kowmung-Wollondilly divide which are treated later. 

In passing, it may be noted that Byrne's Gap, to the east of Mt. Colong, may once 

have been occupied by a stream flowing northwards from the present Tonalli River 

area into the Kowmung. 

An assumption that these great valleys were formed as a result of differential 

erosion in hard and soft strata is not justiflable, not only on account of the 

evidence given above, but also because it would imply that weak streams, such 

as Black Hollow Creek, were capable of great lateral erosion after rejuvenation, 

but before doing much down cutting; and also because the rocks which were eroded 

to form this valley were hard, being Hawkesbury sandstones. Upper Coal Measure 

and Upper Marine Series, which were all littoral deposits. The really soft rocks 

of the area lie on the Kowmung-Wollondilly divide, between Bindook Swamp and 

Mt. Werong, which are highland areas. It is interesting to note that similar 

theories of sharp local warping are being advocated by Mr. Sussmilch for the 

Upper Hunter basin. 

The Extent and External Relationships of the Kotvmung Worp.— So far, field 

evidence has been advanced which has shown, inter alia, that Wallerawang, 

Kanimbla, Megalong, Jamieson's and the Kowmung Valleys were once coextensive 

and have been subjected to differential uplift, so that they are now separated by 

sharp flexures. It is possible to correlate these valley levels, and the earth 

movements producing them, with the levels and movements which produced the 

present Blue Plateau. Text-fig. 12A, which is based on simple mathematical 

projection of broken lines on a fixed line — the latter joining Glenbrook and Mt. 

Lambie, and running in a W.N.W. and E.S.E. direction — shows the relationship 

between the two. Each curve gives the component of the slope along fixed lines 

in the constant direction, and thus shows the folding movements of each line in that 

direction, which latter is generally taken to be the average slope of the Blue 

Plateau Monocline, and is certainly perpendicular to the Kurrajong-Glenbrook- 

Mittagong fold. 

Proceeding eastwards from the Main Divide it is seen that the Piper's Flat- 

Wallerawang Valley is subparallel to the plateau surface, the latter being inter- 

sected by the valley of Cox's Creek. A kink in the plateau surface corresponds 

to a kink in the valley curve, and indicates a relative downthrow area. The 

Hartley flexure has no exact counterpart on the plateau surface, although the high 

ridges at Clarence (not shown) are possibly related. The Kanimbla-Megalong 

levels are parallel to the main plateau. The curve of the Kowmung Warp between 

Mt. Mouin and Jamieson's Creek is distinctly related to the curve of the plateau 

between Woodford and Katoomba. Below Jamieson's Creek the old distinctive 

valley levels end. It is seen that the profiles of the upper valley levels and of the 

plateau are distinctly sympathetic. When one considers that the warping and 

faulting of the Jenolan Plateau have taken place not far to the west of these 

valleys, the correlation is still more striking. Obviously, the earth movements 

which produced the fiexures in the valley floor also affected the plateau surface, 

or, in other words, since the curves show such a striking sympathy of contour, 

they were produced by the same earth movements; that is, the valley levels are 

older than the more recent flexing movements. The nature of the original folds 

which produced the surface in which the valleys were originally incised will be 

shown later. 

This piece of correlation also throws light on the extent of the Kowmung Warp, 

since this warp is clearly shown on the present plateau surface, the eastern edge 

extending across the country between Katoomba and Wentworth Palls, by Mts. 

Hay, Tomah and Irvine, and apparently dying out gradually to the north. A 

definite scarp exists along this line. One result of this is to give Katoomba an 

average annual rainfall of 56 inches, whereas, without the scarp, the rainfall 

would probably not exceed 40 inches. 

The warping may also be correlated with the Nepean Ramp, extending south- 

wards from the neighbourhood of Sydney towards the Shoalhaven River. The 

edge of this warp is not perpendicular to the general north-south line of the mono- 

cline^, but runs to the south-west from (near) Sydney to Picton, where the 

Razorback Range, at the point where this warp crosses the monocline, is probably 

a fault block. 

To the north-west, the hinge is somewhat indefinite towards Oakdale, owing 

to the flattening of the warp and great erosion in the soft shales by tributaries 

of the Nepean, but the southern rise is plainly shown on both sides of the 

Burragorang Valley. To the west of Burragorang, the uplift appears to have been 

more intense, as the plateau to the west at 3,100 feet is 600 feet higher than the 

plateau to the east of this valley at 2,500 feet. It is extremely probable that this 

part of the valley of the Wollondilly has been excavated along a fault line, the 

valleys of Lacy's and Green Wattle Creeks probably following smaller faults. 

I hope to discuss this matter fully in a future paper on the Wollondilly Basin. 

On the east of Burragorang, there is a rise of 400 feet on the plateau from 

the Warragamba to the Nattai Valley, a distance of seven miles. To the west, 

the long ridges between the Wollondilly and Black Hollow Creek rise from 1,900 

feet in the vicinity of the Cox to an average of 3,100 feet on the plateau around 

Mt. Colong over a distance of nineteen miles (Text-fig. 12C), giving an average 

slope of 63 feet per mile. The rise of Kiaramba Ridge from the Cox to Bindook 

Swamp on the Kowmung- Wollondilly divide is 2,500 feet (all of which is not due 

to warping, although most is) over a distance of 23 miles, giving an average 

slope of the order of 119 feet per mile. Thus there is a regular change of slope 

along the lines perpendicular to the edge of the warp as one moves from the 

east of Burragorang to the north of Jamieson's Creek. The average mean slopes 

are of the order, in feet per mile, of: Plateau from the Warragamba to the 

Nattai, 59; plateau between the Cox and Bindook Creek, 63 (Text-fig. 12C) ; 

Kiaramba Ridge in the Kowmung Valley, 109; upper valley slope from Jamieson's 

Creek to Megalong Gap, 280; plateau between Wentworth Falls and Katoomba, 

140 feet. It will thus be seen that the warping reached a maximum of intensity 

to the north-east of Gangerang Range. To the west and south-west of Gangerang, 

the movement of uplift became so intense that faulting took place, as we have 

seen in the study of the Kanangra Platform. The Nepean Ramp-Kowmung Warp 

thus has the general form of a plunging syncline. It will be noted that the 

greatest thickness of Permian and Triassic rocks lies at the focus of the northern 

edge of this syncline; that is, the old Permian and Triassic geosyncline has been 

revived and intensified by late warping movements. 

The latest uplift of Jenolan Plateau, which differentiates it from the main 

Blue Plateau, has already been discussed. A well-marked warp runs from the 

western side of Mt. Lambie to the north of Rydal, and thence on the western 

side of Kanimbla Valley between the Cox River and the main Divide. This warp 

has also affected the eastern part of Megalong Valley to the south of Megalong 

Creek. Still further south, it passes into a fault, which begins near the junction 

of the Cox and Kanangra Rivers and runs parallel to the latter. Indeed, the 

course of this stream and its great canyon have been determined by this fault. 

Continuing to the south of Kanangra Walls, the fault becomes indistinct in the 

soft rocks of the Kowmung-Wollondilly divide, but appears to continue into the 

Wollondilly Basin, and to be connected with the Lake George fault system. I 

hope to discuss this matter in a later paper. 

The physiographic fault at Hartley is, I think, not nearly so extensive as 

this other fault on the west of the Kowmung. Apparently the main warp some 

five miles to the north of Hampton bifurcates, one branch continuing in a less 

intense form to the north, towards Mt. Lambie, the other branch going to the 

north-east across the mouth of Lowther Creek, where it is probably responsible 

for Blaxland's Swamp, and continuing to the west of Hartley, and for some 

distance to the north of the high ridge at Mt. Clarence (up to 4,000 feet). The 

kink in the plateau and upper valley surfaces near Lithgow appears to be a 

part of this earth ripple. In the foregoing discussion, the existence of older 

folds has been kept in the background. Having determined and localized the 

newer earth movements, it is now possible to identify the older folds. 

Turon 

Abercrombie 

No Data for Grose- Colo 

iNepean 

Warra^mba 

an 

Cr 

Vollondillij 

V:H=5a. 

Text-fig. 13. — Pre-uplift Peneplain Surface. 

Primitive folds and basalt residuals are found in meridional lines, with a 

different stream arrangement from that obtaining at the present time. The 

broken line shows the crest of the first extensive fold, which was an anticline. 

The Old Blue (Mt.) Anticline. — The existence of a monoclinal fold in the 

vicinity of Kurrajong and Glenbrook was proved by David. At Kurrajong Heights, 

a maximum vertical displacement of 1,900 feet has been caused by folding dnd 

faulting. Near Glenbrook, the amount of uplift varies from 600 to 800 feet. As 

the fold between Kurrajong Heights and Bent's Basin is composed of hard sand- 

stone, and is of recent formation, it is well preserved. That this fold continues 

to the south is clearly shown by sections of Wianamatta shale near The Oaks and 

at Mowbray Park, between Picton and the Nattai River. To the west, the shale 

is sub-horizontal, but it dips sharply to the east on to the flat country near 

Camden and the more elevated land in the vicinity of Picton. 

To the south of Picton and the west of the Nepean River there is a definite 

dip of the land surface to the east, as the railway heights indicate. The more 

easterly new line through Bargo is, on the average, 150 feet lower than the older 

line io the west, through Picton Lakes and Balmoral. At Mittagong, the mono- 

clinal fold again appears to be present, rising 500 feet above the plain. Mt. 

Alexander, to the north of the town, is composed of sandstones which dip to the 

south at an angle of 11°, according to Taylor. This dip would be sufficient 

to account for the vertical displacement of 500 feet without faulting, although 

it is probable that both folding and faulting are involved. Still further to the 

south, the monocline as a distinctive topographic feature appears to die out. 

The southern portion of the fold is superimposed on the Kowmung Warp and the 

Nepean Ramp. It has already been shown that, between Picton and Kurrajong 

Heights, the face of this monocline is of recent development. The old eastern 

face of the main Blue Plateau uplifts was from three to six miles to the west, 

and the fold had a much more uniform slope at its base, as the Mulgoa Step had 

not been formed. From Razorback southwards, however, it is probable that the 

original fold face is preserved. The nature and extent of the first folding move- 

ment may be determined by subtracting the later movements from the sum total. 

This is readily done by reducing the Kowmung-Kanimbla-Wallerawang Valleys to 

their original level. We have already seen that all of these valley floors were, in 

the past, co-extensive. By flattening out the later flexures, therefore, the original 

contour of what is now the plateau surface will be obtained, as in Text-fig. 14. 

At Wallerawang, the plateau surface was 600 feet above the local base-level 

of erosion (not 600 feet above sea-level) ; Kanimbla Valley was entrenched 1,200 

feet in the plateau surface, Jamieson's Valley, 1,500 feet, and the Kowmung Valley 

from 1,400 feet at the Cox junction to 400 feet at Bindook Swamp. Thus the 

surface takes the form of an asymmetric anticline (Text-fig. 14), with a steep 

eastern limb and a gently sloping western limb. It attained a maximum elevation 

of 2,000 feet along the Bilpin-Hazelbrook-King's Tableland line, which step con- 

tinued across the present Lower Cox Valley, and is still found to the east of 

Burragorang Valley. 

If a hinge or line of folding were developed along some part of an asymmetric 

anticline, near the crest, and the limb of the original fold away from the hinge 

and the crest were uplifted, then that part of the fold adjacent to the original 

crest of the anticline, and along the new hinge, would be rather flattened, that 

is, its curvature would be decreased. That is to say, there would be a change of 

slope — or "step" — in the flnal fold curve near the position of the crest of the 

original anticline. 

That such a position has arisen in this region is shown by the topography 

of the plateau surface. The land near the crest of the old anticlinal fold is now 

represented by the Bilpin-Hazelbrook-King's Tableland step at 2,200 feet. That 

this step was the crest of the old fold is clearly shown by the decreasing depth 

of the upper valleys as one goes to the west (Text-fig. 12), and by the still- 

existing uniform slope to the east. This theory has four specific advantages: — 

1. It explains the erosion of the great Jamieson s Valley almost to the Grose 

Divide, and the formation of the Lower Cox and the Burragorang Valleys. All of 

these are located on, or near, the supposed anticlinal crest, which would be the 

main line of weakness and erosion. The continuous and almost straight line of 

these valleys is most striking. It is also notable that the Kowmung Valley is not 

included in this system. 

2. It also explains the peculiar topography of the King's Tableland, which 

can only be mentioned briefly here. A number of small streams rise on this step 

and flow westwards into Jamieson's Valley, rising in broad, swampy mature 

valleys between 1,800 and 2,000 feet. They plunge into the higher land from 

-Vol^an 

Warragamba 

Nepean 

WollondJllij 

Natbai vH=ab 

Text-fig. 14. — The Old Blue Mountain Anticline. 

The old anticline had a steep eastern face, but sloped gently to the west. The 

heights given are above the local base levels of the respective districts. The 

elevation of the western portion (marked 600 feet) was probably of the order 

of 1,000 feet above modern sea-level. The central heights are approximately 

correct on both standards, as are the eastern. 

2,200 to 2,300 feet before entering the valley, flowing through narrow little gorges. 

They appear to be antecedent, and their swamps may have formed by the partial 

blocking of the streams caused by a slowly-rising barrier to the west — the newer 

fold, or Kowmung Warp. I hope to discuss this more fully in a future short 

paper. 

3. The formation of the Nattai Valley is explained. At the present time the 

Nattai is a misfit, trickling over the floor of a big valley. The cliff walls are much 

cut up and dissected, in strong contrast to the straight, new cliffs of Burragorang. 

As the Nattai shows small meanders such as are not found on the lower Wollon- 

dilly, its valley is also older. This agrees with the previous conclusion that the 

latter is a recently-formed stream, its position being determined by the location 

of the old anticlinal crest. This point will be further discussed later. 

4. Such a fold as is postulated in Text-fig. 14 accounts for the very extensive 

dissection of the hard rocks which has been accomplished by Erskine, Glenbrook 

and Euroka Creeks, the Grose River and its tributaries, the Colo system and the 

Nattai. The country which was more affected by the later warping and folding, 

although now more elevated, has not suffered anything like the same degree of 

dissection. Again, the newly-raised Nepean Ramp and the Southern Tablelands 

around Goulburn are comparatively little dissected. In general, the mature valley 

systems (Kanimbla, etc.), which have been described, fit in very well with this 

theory. 

Turon-Cox- Ko\ymun$$ 

Valler ^ 

Blue Plabeau 

Jenolan ^ 

Plateau"^ 

Kanaq^ra 

Plateau 

Ko\wmun 

\)/arp 

Kurrajon^ - Glenbrook - 

' litta^ofg- Monocline 

, Sbillstand 

Varra^amha Coige 

Nepean "Ramp 

Text-fig. 15.- — Analysis of the Fold Systems (generalized). 

The principal modern tectonic features of the region are here summarized. 

Overlapping of folds gives greater elevation, so the most elevated part (Jenolan 

Plateau) has undergone three uplifts. The superposition of the old anticline on 

the Kowmung Warp, and its effect on the altitude of that part of the region 

are shown. This is an extension and generalization of Text-fig. 2. 

Scale : 1 inch = 30 miles. Cox divide shown thus . 

Text-figs. 13, 14 and 15 show the whole process of folding which the Cox Basin 

has undergone. Text-fig. 13 is further discussed later. Text-fig. 14 is a restoration 

of the old anticline, based on the data shown in Text-fig. 12, whilst Text-fig. 15 

shows the principal modern features of the topography, and summarizes the 

conclusions as to the nature of the post-basaltic earth movements which have 

affected this area. The northern edge of the warping and folding movements which 

uplifted the southern highlands of this State is represented by the Kowmung Warp. 

The southern edge of the main northern uplift is represented by the Hornsby Warp 

across the Hawkesbury, and the old anticline. 

Direction of Forces Causing Uplift. — ^Whilst it is very unsafe to base any 

very general conclusions as to the direction of forces causing these uplifts on the 

evidence offered here alone, a few suggestions might not be out of place. There 

is, I think, very little evidence to justify the possible suggestion that the uplift of 

this region is largely the result of purely compressive (tangential) forces. On 

account of the general low angular value of the warping movements, the absence 

of great overthrust faults, and the formation of purely plateau topography, the 

forces of uplift would appear to have been, in the main, normal to the surface of 

the earth. This would involve a certain amount of compression, as two normal 

forces at different points would give rise to a certain resultant tangential force. 

It has been suggested that the uplift of this plateau was the result of forces 

acting from the Pacific. Alternatively, another opinion has been expressed that 

the later phases of uplift were largely caused by forces from the west. A tentative 

conclusion might be, that the principal uplifts were the result of normal forces, 

and the tangential forces which they set up acted mainly from the west, although 

forces acting from the east were not unknown. 

Streams of the Area. 

Stream Characteristics and Relationships. — The general characteristics of the 

streams of Eastern Australia have been outlined by Taylor (Physiography of E. 

Australia), who has discussed many specific anomalies of flow. These streams 

fall into two main classes — longitudinal and transverse. The first class includes 

many of the tributaries of the Upper Murrumbidgee, the greater part of the 

Wollondilly, Shoalhaven and Nepean, the Upper Cox and some streams of the 

Upper Hunter. Such streams as the lower parts of the Clyde, Shoalhaven and 

Hawkesbury, the Upper Abercrombie and Turon, the Grose, Colo, Goulburn and 

Lower Hunter Rivers may all be classed as transverse streams. In general, each 

main river system includes many streams of each type, but the highly irregular, 

meandering courses throughout their lengths of the composite rivers give evidence 

that the present anomalous arrangement is, in general, of some age. 

In the Cox Basin itself the streams fall naturally into two classes, according 

to geographic distribution. Those in the western part of the area, such as the 

Cox above Jamieson's Creek, the Kowmung, Tuglow, Upper Wollondilly Rivers 

and many smaller streams flow in highly irregular meandering courses (Text-figs. 

4 and 8), although, for the most part, they are now entrenched in deep canyons. 

These meanders have been inherited from earlier cycles. The eastern streams, such 

as the Lower Wollondilly, Warragamba, Lower Cox and, a little to the north, 

Erskine Creek and Grose River, do not show meanders. They are generally 

straight, with bends and curves of low angular value. In fact the main river — 

the Warragamba^is absolutely straight for nine miles of its fifteen-mile course. 

These streams are quite different from, and of much more recent formation than, 

those of the first-mentioned class, which show structural affinities with the ancient 

rivers of the Western Slopes, the Macquarie and Abercrombie. On these grounds 

one might reasonably believe that the Western Cox Basin once belonged to the 

Western stream system. 

The Cox River Basin occupies an oval-shaped area at the centre of a radial 

drainage system. Many of the main streams of east-central New South Wales 

rise on the Cox watershed. They include the Grose and Colo Rivers, the Turon, 

Campbell and Fish Rivers of the Macquarie system, the Abercrombie River, and 

tributaries of the Wollondilly and Nepean. At first glance it might be thought 

that the Cox is a simple consequent stream, whose origin is directly traceable to 

the uplift of the Blue Plateau and which has eroded its present complicated series 

of canyons directly in that surface, enlarging itself at the expense of surrounding 

streams. Field evidence is quite against this, as the Upper Cox itself is threatened 

with capture in places, and that part of its basin is in a state of siege. 

Divides of the Cox. — In places where the original plateau surface is well 

preserved, such as Katoomba, Hampton, Shooter's Hill, and King's Tableland, the 

divide is comparatively wide and flat. It is the remains of an ancient peneplain, 

dissected to a depth of 200 feet by mature valleys, the direction of short streams 

being largely determined by local geological structure. To the north and north-east 

of Lithgow, for example, the influence of two perpendicular sets of master joints 

has given the streams a trellis pattern. The small cores of undissected country 

on the eastern and southern divides are being attacked by steep streams on 

either side of the watershed. At some places local captures are pending, as 

Wentworth Falls (Taylor), and also near Mt. Werong, where Werong Creek, of 

the Kowmung system, has captured part of the head of the Abercrombie on an 

ancient plain. 

The Main Divide between Rydal and Jenolan is a high ridge flanked on 

either side by sub-mature valleys. Here there is no prospect of any marked 

stream readjustment. 

In other places the divide is very unstable. At Wolgan Gap it has been 

breached, and Cox's Creek rises above a yawning valley in which the Wolgan 

River flows, 1,200 feet below. Capture of the high stream has proceeded to some 

Mt^^lber 

Cox River 

^'--.librc 

Mt. Lambie 

4I0O 

Tribuharics 

of the CO% 

Text-ng. 16. — Solitary Creek. 

Note the high-level valley of the Creek, and the steep canyon of the Cox. The 

high-level valley of the Cox between Rydal and Mt. Walker is shovs^n, and the 

meanders of the Cox. Solitary Creek is on the point of capture. Note the 

small antecedent tributary on the west in the diagram. Scale : 1 inch = 2 miles. 

extent. Again, at Piper's Flat the Main Divide is represented by a ridge which 

rises forty feet above the plain, and is about a quarter of a mile wide. This runs 

across a valley four miles wide and 400 feet deep, and appears to be a local fold 

in shale. On the northern side Dulhunty's Creek, a tributary of Williewa Creek 

(Turon), is flowing at a lower level than Piper's Flat Creek, and with a steeper 

grade — 100 feet per mile as against 30 feet. It is cutting back in the soft ridge, 

and threatening to capture Piper's Flat Creek. A few miles to the north the head 

of Gow's Creek, flowing in a broad valley at 3,500 feet, is being captured by a 

small tributary of Solitary Creek. Here a slight change only is involved. Two 

great breaches in the western divides, at Rydal and Bindook Swamp, call for 

special attention. 

Solitary Creek.- — Solitary Creek (Text-figs. 4 and 16) rises on the northern 

side of Mt. Lambie and, turning, flows southwards through Rydal and later, with 

the Fish River, pursues a westward course through Bathurst, thus forming part 

of a spiral. Between the Lambie block and Mt. Walker the upper valley surface 

of the Cox is prominent at 3,100 feet, stretching south to the scarp near Hartley. 

Immediately to the south-west of Solitary Creek Plain between Wallerawang and 

Rydal, a continuous scarp rises, which is a continuation of the "Western Kanimbla 

Warp. A small tributary of Solitary Creek flows into the warp (right centre. 

Text-fig. 16), whilst a little lower down Solitary Creek flows across the warp line 

on to a plain, re-entering the higher scarp just above Rydal. Six hundred feet 

below, and only two miles away, the Cox flows in a juvenile gorge sawn in 

tremendously hard quartzite, whilst steep tributaries are threatening to capture 

Solitary Creek from the east and north. Immediately to the north of Rydal the 

Main Divide is only half a mile from the creek, and fifteen feet above it, the valley, 

along which the Western Railway runs, being quite continuous. The Cox shows 

very fine meanders in extremely hard rock, and so must have followed its present 

course before the cutting of its modern trench. On the other hand, it is not 

possible that Solitary Creek should have maintained its present relative course for 

long, since tributaries of Piper's Flat Creek, but slightly rejuvenated, are in the 

course of capturing it. The presence of the continuous Wallerawang-Rydal Valley 

and the boathook bend of Solitary Creek, together with the age and power of the 

main river, show that some stream change has taken place. A reconstruction of 

the topography when the Wallerawang and Kanimbla levels were co-extensive is 

instructive. Then the Cox flowed sluggishly over the plain floor of its valley. 

The local "kink" in the valley floor and the plateau near Wallerawang (Text-fig. 12) 

could not then have existed, as it is lower in the valley than the contemporaneous 

valley levels on all sides at 3,000 to 3,200 feet. At that time Solitary and Piper's 

Flat Creeks, and the Main Divide at Piper's Flat were on much the same level. 

Later, probably in conjunction with the fault at Hartley, the area around Wallera- 

wang lagged behind a little in the continuous uplift, forming a small tectonic 

hollow. Uplift and tilting of the Wallerawang Valley took place towards the west 

and south-west. Piper's Flat now has a grade of 30 feet per mile, and is being 

eroded. Experience shows that streams — e.g., the Lower Cox and Wollondilly — 

erode previously deposited alluvials when flowing at a grade of only ten feet per 

mile. Piper's Flat, now being eroded, could not have been formed at its present 

slope. At the same time, the Cox could not have readily captured Solitary Creek, 

as it had not then its present advantage of grade. But to suppose that Solitary 

Creek at that time flowed as it does now, leaves unexplained the great Wallerawang- 

Rydal Valley, which is quite dissimilar to other valleys of tributary streams just 

to the west, and has been carved in hard conglomerate and quartzite by stream 

action. Also, the anomalies of the present Main Divide — here partly valley, partly 

slope divide — are not explained. 

On account of the permanence of the Cox, one is forced to the conclusion 

that a stream once occupied Wallerawang-Rydal Valley, and flowed from Rydal 

to the Cox. This would place the Main Divide near Tarana, and might include 

Antonio's Creek, which runs northward into Solitary Creek and parallel to the 

Main Divide, in the Cox system. This old Divide would have passed in a normal 

manner over Mt. Lambie, and would have consisted of very soft, decomposed 

granite, similar to that at Sodwalls. After the inception of the present topography, 

but before the sagging around Wallerawang, the Fish River and its tributaries, 

tearing back through the soft granite, captured Solitary Creek near Tarana. Then 

the Cox, being rejuvenated in this part, cut back past Mt. Walker, and the slight 

sagging around Wallerawang gave the small tributaries of Piper's Flat Creek 

a higher grade than previously, so that now Solitary Creek, entrenching slowly, 

is threatened with recapture by the Cox. The thalweg of Solitary Creek below 

Rydal supports this theory. The head of entrenchment is at Rydal. The grade 

from here to Tarana (12 miles) is 50 feet per mile, whilst from Tarana to 

Bathurst, Fish River has only a grade of 11 feet per mile. The steepest portion, 

between Rydal and Sodwalls, just above Antonio's Creek, has a grade of 70 feet 

Lanni^arfs Cr 

So'am 

BindoobCr 

3200 

Text-flg. 17.— The Breached Divide at Bindook Swamp. 

Lannigan's Creek is on the point of capturing the high-level swamps. Note the 

erratic course of Bindook Creek, and the sandstone residuals in a late mature 

valley. 

per mile. Considering these figures, and the softness of the decomposed granite, 

one concludes that the tributary of Fish River, flowing at a low level, was quite 

competent to capture Solitary Creek from the Cox when the latter was at a 

standstill. Rejuvenation has since moved upstream from the supposed ancient 

divide. Thus Cox River is now about to recapture Solitary Creek. 

Bindook Sioamp. — Bindook Swamp lies on the Kowmung-Wollondilly divide 

four miles south-west of Mt. Colong. The swamp lies in a great level valley, 2,800 

feet above the sea, to the east and west of which the plateau rises to an elevation 

of 3,200 feet, and is cut in sandstone (horizontal) and slate (Text-fig. 17). Two 

isolated sandstone hills are left in the valley, which is cut in very soft Silurian 

strata. Bindook Creek flows north over a level valley to within a couple of 

hundred yards of the divide, which is only a few feet above the stream and is 

absolutely flat. It then turns south, and flows to the Wollondilly. This condition 

of affairs is obviously transient, as Lannigan's Creek is on the point of capturing 

Bindook Creek. The gap in the divide is three-quarters of a mile wide, and the 

valley of which it is part is mature to late mature in type. It forms a link 

between the Kowmung Valley on the north and the Wollondilly Valley on the 

south. It represents at present an air gap in the divide formed by stream 

erosion. The relationship of this to the Kowmung and Wollondilly is discussed 

later. 

Cox River and Its Trihutaries. 

Relative Stream Ages. — The general classification of streams into a newer 

and an older type has already been mentioned. This classification would, how- 

ever, fall to the ground if ancient streams following meandering courses were 

to assume meandering courses subsequent to uplift and rejuvenation. But such 

ancient streams will continue to enlarge their meanders after rejuvenation, as 

tangential horizontal forces still act at the bends, eroding on the convex stream 

bends and causing the channel to migrate. Fine examples of these meanders 

enlarged by a revived stream flowing down a warp are observed on the Cox near 

Jamieson's Creek. The long straight courses of the Lower Wollondilly and the 

Warragamba especially, which are consequent streams, and the straight character 

of their gorges, with a slight overlapping of spurs, indicate that they are certainly 

newly-formed streams. Many similarly revived streams in this region — the Colo 

and Macdonald, for example— have preserved fine meanders, and it does not seem 

reasonable to suppose that such a straight stream as the Warragamba, flowing 

under exactly similar conditions to the Colo and Macdonald, could have divested 

itself of all traces of antiquity since uplift. It will be seen that these newer 

streams are confined to deep valleys and gorges on the eastern side of the Cox 

Basin. 

The great valleys of the Kowmung and Cox, from eight to fifteen miles wide, 

are occupied by ancient streams. The meanders and horseshoe bends of these 

streams are not local features, but are found in all varieties of rock types, 

including horizontal and tilted shale and sandstone, highly-inclined slate and 

quartzite, and porphyry and granite. The amplitude of the bends varies inversely 

as the hardness of the rocks in which they occur, but the actual type and character 

do not change. 

The actual form of the valleys of such streams as the Lower Wollondilly and 

Green Wattle Creek suggests that they are of recent formation. For mile after 

mile the sandstone cliffs fianking the eastern sides of parts of these valleys are 

absolutely straight, and are known as Burragorang and Green Wattle "Walls" 

respectively. They are hardly notched at the top and show no embayments. 

No tributary streams come over these cliffs to the main streams below. The cliffs 

of Jamieson's and Grose Valleys are deeply embayed on all sides, and deeply 

notched at close intervals, even where mere wet-weather streams cross them. 

These walls are, generally, less than a mile from the river, as close as are the cliffs 

of the Grose to their river. This would seem to indicate that these walls and the 

valleys which they flank are of very recent development. For a few miles on the 

western side of the Wollondilly around Byrne's Creek and Tonalli River much more 

erosion has been accomplished, but this may have been initiated by streams 

flowing westward through the present air gaps near Yerranderie to the Kowmung. 

The levels of the passes seem to indicate this. 

In the case of the Lower Cox Valley, the river above King's Tableland shows 

characteristic meanders, but downstream these do not appear. Just where the 

river crosses the King's Tableland-Tonalli scarp a great double "S" bend has 

been developed on a small unwarped plain just above the scarp. This feature 

is of recent origin, and is quite different from other Cox meanders, not being 

fully developed. 

The Kowmung-Jamieson's Valley stretches from Wentworth Falls to Bindook, 

and from King's Tableland to Gangerang Range, having a north-south length of 

30 miles and an east-west width of eight miles. The eastern outlet is a gap in 

the rocky walls less than a mile and a half wide. As the Kowmung Valley has 

been cut in a series of rocks similar to, although somewhat harder than, those 

of the Lower Cox Valley, an explanation by differential erosion, particularly in the 

light of the warping indicated, is out of the question. Also the Cox Valley 

below this point is quite juvenile. Even the overlapping spurs are preserved. 

The Lower Wollondilly has every appearance of having developed along a 

fracture or fault of a linear character. This is not the case with the Nattai, 

which has a rather tremulous appearance, and is probably an old stream preserving 

part of its original course, although part has been wiped out by newer streams. 

Werriberri (Monkey) Creek, which is not much entrenched on the average, and 

has remarkably few tributaries, also appears to be a relic of an old meridional 

stream which has been deprived of most of its water by newly-formed streams. 

Thus the Upper Wollondilly-Kowmung-Upper Cox form an old stream line, whilst 

the Lower Cox-Wollondilly is of much more recent formation. 

Anomalies of Direction.— A survey of the Cox basin shows many anomalies 

in the direction of stream flow. The normally-branching type of stream is almost 

absent, and the whole pattern is curiously twisted. Many of the streams are 

subsequent, being largely determined by rock strike. Hollander's and parts of 

the Tuglow Rivers, Mumbedah Creek, Breakfast Creek, Marangaroo Creek and 

many smaller streams come under this heading. The Kowmung runs partly along 

the strike of the Devonian beds, and also probably follows an ancient fault. 

A number of the tributary streams join the Cox in an upstream direction. 

Lowther, Farmer's, Lett, Mumbedah, Kanangra Creeks, the Kowmung and Little 

Rivers are good examples. These, especially the first-named, which flows in 

granite, may be due to a former westward drainage. The great arc of the 

Hollander-Tuglow is parallel to lines of basalt residuals strung along the Kowmung- 

Wollondilly and Main Divides between Shooter's Hill, Oberon and Yerranderie. 

Residual streams flowing just along these divides are also parallel to the main 

arc. The basalt flows, now almost obliterated, appear to have influenced these 

streams, which are also parallel to the general rock strike. 

The Kowmung Basin in particular is asymmetric. It receives no tributaries 

of note from the east, owing to the proximity of the Black Hollow Creek divide 

in the main upper valley. Air gaps in the Tonalli Range to the east, however, 

may indicate the former flow of westward streams into the Kowmung, which 

might also have received streams from the present area occupied by Black Hollow 

Creek before the last phases of uplift caused a longitudinal channel to form 

along the warp in the eastern part of the valley. Mature relics of valleys on the 

Kowmung-Black Hollow divide indicate such a possibility. The Warragamba is 

also asymmetric, as its northern divide is less than four miles from the river. 

Parts of the Lower Wollondilly are also similar in this respect. 

As the streams flow at present, boathook bends, especially that of the Tuglow- 

Kowmung line, are not at all rare. It is quite impossible to suggest a scheme of 

stream flow in the past, and post-basaltic, which would be theoretically normal and 

fit in with observed physiographic facts. It is considered, therefore, that this 

stream system has been abnormal over a considerable period of time, and its 

evolution has been determined by very many factors — normal erosion, geological 

structure, vulcanism and tectonics all having been prominent. 

Relationship between the Kowmung and Wollondilly. — The remarkable breach 

in the divide between these two streams at Bindook Swamp has already been 

discussed. The asymmetry of the divide is notable, as it is nine miles from the 

Wollondilly and three miles only from the Kowmung. A large area of the 

Bindook Swamps and level valleys of the former system, extending three miles 

south of the divide, is in danger of imminent capture by the Kowmung. 

This is the only notable gap in the divide between Mts. Colong and Werong, 

although numerous narrow gaps occur in the soft Silurian rocks along the divide. 

The gap becomes even more significant when the course of the Wollondilly is 

studied. At the junction of Murruin Creek — into which Bindook Creek empties 

itself — with the Wollondilly, the river turns through 120 degrees, forming the 

"Murruin Elbow," flowing eight miles in an easterly direction before resuming 

a northward course. The character of the river also changes at this bend. Above 

here it swings backwards and forwards in great meanders, which are cut in a 

canyon 2,000 feet deep. Below the elbow the river has few bends, these few 

certainly not being meanders. As in the case of the Cox, this indicates different 

ages for two sections of the stream. The case of the Wollondilly is the more 

impressive, however, because the character of the gorge does not change here, 

the deep, broad canyon persisting far upstream. 

To the north of the divide at Bindook the ancient Kowmung flows, also 

sweeping past this point in a great turn. Unlike the Wollondilly it shows 

meanders both above and below the bend. 

The conclusion is, that before the uplift of the Blue Mt. Anticline (here 400 

to 600 feet), the Upper Wollondilly and the Kowmung formed a continuous stream, 

which was broken up by capture, giving the present arrangement. This stream 

line is post-basaltic in age, as it cuts across the line of old basalt residuals. 

Apparently at one time the basalt extended continuously along this divide. If 

that is so, the Upper Wollondilly, Kowmung and Cox originated in Late Tertiary 

times, and developed their meandering structure after the basalt flows, and before 

the first uplift of the old anticline. 

History of the Stream System. — The conclusion has already been reached 

that the Kowmung, Jamieson's, Kanimbla and Wallerawang Valleys were once 

coextensive near base level. The conclusion that the original uplift was here of 

anticlinal form with the crest near the King's Tableland-Lower Wollondilly line 

leads one to the corollary that this great valley was cut in the western flank of 

the fold. The depth varies from 400 feet at Bindook Swamp to 1,500 feet near 

King's Tableland, gradually shallowing to 1,200 feet in Kanimbla and 500 feet 

near Wallerawang. The continuous valley opening out from Piper's Flat into the 

Turon Basin could not have been entirely eroded by the streams now occupying 

it (cf. Cox's Creek Valley). The line of gravels also points to the presence of a 

large stream, which once flowed over the present Main Divide.

 The evidence of relative age of the various streams proves that the stream system

 had no outlet to the east. In view of all these facts, then, it appears that the Upper

 Wollondilly- Kowmung-Cox flowed to the north-west into the Turon before the

 initiation of the posL-basaltic uplifts. 

After the uplift of the anticline numerous consequent streams, such as 

Erskine Creek, Grose River and the Warragamba, were formed on its steep 

eastern face. These obliterated the old (feeble) drainage, leaving only a few 

relic streams, such as Werriberri (Monkey) Creek and the Nattai. Pushing back 

along joint planes, and possibly along fracture lines, these streams cut through 

the hard plateau sandstones and found the soft Coal Measure shales beneath, 

rapidly enlarging their valleys. In this way the valleys of the Lower Cox and 

Wollondilly, Lacy's and Green Wattle Creeks and the Nattai were formed. The 

valleys of the smaller streams are surprisingly large and well graded, and do not 

compare unfavourably as regards size with the Wollondilly Valley (Burragorang) 

itself. This is further evidence that the latter was not always occupied by a 

large stream. Thus before the initiation of the main Kowmung Warp these 

streams were attacking the divides of the old Kowmung line to the west. 

When the Kowmung Warp commenced, the flow of the Cox was considerably 

retarded, as the river was pushing against the uplift. The Kowmung and Upper 

Wollondilly were thrust up, but were not able to cut down very much, on account 

of the hanging up of the Cox. Thus the low-lying Lower Wollondilly, cutting along 

lines of weakness, was enabled to capture the high-level, sluggish Upper Wollon- 

dilly, and to push back the new divide at the expense of the Kowmung. The 

Lower Cox River, which had previously almost obliterated the divide between it 

and Jamieson's Valley, continued this erosive work, and the middle Cox and 

Kowmung being quite unable to hold to a northward flow against the rapidly 

rising warp, were, in course of time, captured and reversed. That the Kowmung 

was able to keep to its original course is shown by its antecedent nature before its 

junction with the Cox. 

During this time the flexure at Hartley had been developing, cutting the Upper 

Cox off from the Kanimbla streams. The Upper Cox, flowing over Piper's Flat, 

deposited the older gravels. Using Kanimbla Valley as a base-level of erosion, the 

Cox above Hartley began to trench its upper course and gradually the whole of 

the river was reversed. Before this took place, Upper Solitary Creek had been 

captured and reversed by a tributary of Fish River. The stream flowing along 

Piper's Flat being reversed, it began to cut into the older valley a little, forming 

the modern "Piper's Flat", extending from Wallerawang to the present Main 

Divide. A slight sagging of the crust around Wallerawang, together with some 

tilting towards Mt. Lambie, caused this flat to dip east, and revived the streams 

flowing along it, causing erosion of the flat, which is now proceeding, and 

allowing small tributaries to attack the valley divide of Solitary Creek. 

At the head of Cox's Creek, Wolgan River, which had been considerably 

affected by the old anticline, had cut through the Hawkesbury Sandstone — here 

fairly thin — and had cut a great gorge in soft underlying Coal Measure strata. 

At the present time Cox's Creek is being gradually captured. 

Since these various stream changes have taken place, the Upper Wollondilly 

has been able to cut back, and is now entrenched as far upstream as Paddy's River. 

Kowmung River has cut a profound canyon up to 2,000 feet deep almost to its 

head, and small tributaries are capturing Bindook Creek, tending to make the 

 divide here more symmetrical. Marked asymmetry of this divide was caused, 

in the first place, by the captured Upper Wollondilly being able to cut back in the 

old high-level valley before the Kowmung was rejuvenated to the great bend. 

Cox River has cut two series of great canyons, between Wallerawang and Hartley, 

and between Megalong and Jamieson's Creek. At the present time the stream 

system is in a state of neutral equilibrium, and only comparatively small captures 

are pending. 

These conclusions have been previously arrived at, in part, by Taylor, who 

postulated a westward flow for the Cox-Wollondilly. This paper varies his 

conclusion by suggesting the Upper Wollondilly-Kowmung-Cox as the old stream 

line. 

With regard to the streams of the Nepean system, there is no evidence that 

they have drained into the western rivers since the commencement of the folding 

which caused the Blue Mountain anticline. Such a direction of flow, as Taylor 

has suggested in his papers, was possible before the commencement of this series 

of uplifts, although I rather incline to the opinion that the Nepean, Cordeaux, 

Cataract and Avon are comparatively recently-formed streams of consequent type. 

Taylor's theory of the formation of Kanimbla Valley in the western side of the 

first fold is definitely established. 

Past History of the Area, 

a. Earth Movements. 

Silurian. — Subsidence. Deposition of sedimentary rocks, since metamorphosed. 

Now found in western part of area as slates, claystones, limestones, etc. 

Vnconformity. 

Devonian (Lower?). — Further subsidence. Deposition of shales, sandstones, con- 

glomerates, etc., since largely metamorphosed to quartzites, slates, etc. 

Devonian? or Carboniferous. — "Kanimbla Epoch". Great folding and mountain 

building movements. Intrusion of batholith of granite, with sills and dykes 

of quartz-porphyry. Regional metamorphism. Erosion.

Carboniferous. — Great cycle of erosion. Granite exposed and a peneplain formed. 

Great Unconformity. 

Permian. — Subsidence and deposition of Upper Marine Series. Present Jenolan 

Plateau just below sea. Formation of Coal Measure swamps. Deposition 

of Upper Coal Measures. Continued subsidence. 

Triassic. — Deposition of Narrabeen and Hawkesbury beds conformable with 

Permian. Deposition of Wianamatta Shale to east. Since the close of 

Triassic, dominant movement here is of uplift. 

Cretaceous.- — ^*Uplift and Peneplanation (?). (Sussmilch). 

Tertiary (Lower and Middle). — Formation of peneplain. Old rivers, since 

obliterated by basalts, formed. 

*Slight subsidence and deposition of river leads. 

Slight uplift and basalt flows (Older Basalt). 

Tertiary (Upper) (Physiographic Record). — Erosion. Outpouring of the Newer 

Basalts (e.g. Robertson). 

Formation of great peneplain. Present plateau surface. 

Cox-Wollondilly systems take form. 

Slight uplift. Valleys of Wentworth Falls type. 

* Signifies no reliable evidence in this area. 

Post-Tertiary? — Uplift to the north. Formation of old Blue Mountain Anticline. 

Post-Tertiary. — General uplift to south and west. Kowmung Warp and Jenolan 

Dome. 

Hartley fault and Mulgoa-Kurrajong "Step". 

Recent. — Canyon Cycle. Erosion of great canyons still proceeding. 

h. Stream History. 

Upper Tertiary. — Upper Wollondilly-Kowmung-Cox formed. Late mature valleys 

gave meandering courses. 

Eastern streams (Nattai, etc.) flow northwards. 

Blue Mt. Anticline. — Kowmung-Kanimbla-Wallerawang Valley cut in fold. 

Formation of consequent streams — Lower Cox-Wollondilly, Warragamba and 

Grose. These eroded deep gorges. 

Older gravels, Piper's Flat (?). 

Kowmung Warp. — Capture of Upper Wollondilly by present Lower Wollondilly. 

Capture of Middle Cox and Kowmung by present Lower Cox. 

Reversal of Cox in Kanimbla Valley. 

Capture of Upper Solitary Creek by Fish River. 

Hartley Fault. — Cox forms canyons above Hartley. 

Modern Piper's Flat formed. 

Slight depression near Wallerawang. Upward movement towards Mt. Lambie. 

Solitary Creek threatened with capture. 

References. 

Andrews, B. C, 1903. — Geography of the Blue Mts. and Sydney District. Proc. Linn. 

See. N.S.W., xxxvii, 986. 

, 1910. — Geographical Unity of Eastern Australia. Proc. Roy. Soc. N.S.W., 

xliv, 420. 

David, T. W. E., 1896. — Anniversary Address. Proc. Roy. Soc. N.S.W., xxx, 33. 

, 1902. — An Important Geological Fault at Kurrajong Heights. Proc. Roy. Soc. 

N.S.W.. xxxvi, 359. 

Davis, W. M., 1898. — Physical Geography, p. 282 (Ginn & Co.). 

— , 1909. — Geographical Essays, pp. 413-484, Rivers and Valleys of Pennsylvania 

(Ginn & Co.). 

Fenner, C, 1918. — Physiography of the Werribee River Area. Proc. Roy. Soc. Vict., 

xxxi (N.S.), 33. 

Hedley, C, 1911. — A Study of Marginal Drainage. Proc. Linn. Soc. N.S.W., xlvi. 

Taylor, G., 1911.- — Physiography of Eastern Australia. Bulletin 8, Commonwealth 

Meteorological Bureau. 

, 1918. — The Australian Environment. Memoir 1, Advisory Council of Science 

and Industry. 

, 1923.^ — The Warped Littoral Around Sydney. Proc. Roy. Soc. N.S.W., Ivii, 58. 

,1923a.. — Guide Book to Excursions to Blue Mts., etc. Pan-Pacific Science 

Congress, Sydney, 1923. 

EXPLANATION OF PLATES XIX-XX. 

Plate xix. 

1. Piper's Flat. View from the Main Divide showing the asymmetric valley ; the 

modern silt flats ; and the site of older gravels in middle distance. 

2. Silt Flats, Blackheath Glen, Megalong Valley. Note the sharp rise of the talus slopes 

from the level plain. 

Plate XX. 

1. Walls of Green Wattle Creek. The flat in the foreground at 400 feet contains rounded 

pebbles. The straight walls are unbroken for some miles. 

2. View up Burragorang Valley. Wollondilly on right and Nattai on left. The valley 

is approaching maturity. Note the peak residuals on the edge of the cliffs. These are 

arranged along north-south lines.