|Page tools: Print Page RSS Search this Product|
This page was updated on 23 Nov 2012 to include the disclaimer below. No other content in this article was affected.
In the extreme south-east of the State are the low volcanic cones (600 to 700 feet) of Mount Gambler. A number of small lakes, usually due to subsidence, are associated with the cones. It seems probable that their water supply is derived from permeable beds extending well into Victoria.
The State can be divided broadly into two regions, the Western Lowlands largely consisting of the plains covering the Artesian water-bearing beds, and the Eastern Cordillera, which extends in a belt some 200 miles wide along the coast. There are, however, several subdivisions.
2. Selwyn Upland
To the west of Cloncurry is a belt of uplands, including, the Selwyn Range, which consists of ancient rocks forming the boundary of the Mesozoic Artesian Series. These rocks are on the whole siliceous and mineral bearing, and contain such well-known fields as Mount Isa and Duchess. They form part of the main Divide, but consist in places of meridional ridges running more or less across the Divide. Towards Camooweal occur interesting dolines (or deep hollows) in the porous massive limestones. The Golf rivers rise in perennial streams flowing from similar limestones.
3. Great Artesian Basin
This well-defined geological feature extends into four States, but more than half of the total area is in Queensland. The water-bearing layer is at varying depths; outcropping on the east along the Divide, and sinking to 1,000 feet below the surface, near Blackall on the Barcoo River. There is another localized depression over 3,500 feet deep near Mungindi. (These deeply seated waters flow out to the surface along the western edge of the basin, in the form of hundreds of mound springs, especially between Lake Frome and Oodnadatta).
The surface of this region is a vast plain almost wholly below 1,000 feet. Indeed, except along the eastern margin, nearly all of it is below 500 feet, but near Kynuna an east-west belt forms a low ridge (above 500 feet) right across the northern part of the basin. Other lower ridges separate from each other the broad alluvial-filled valleys of the Diamantina, Thomson, and Baron. These rivers flow only after heavy rains, but in flood time they are many miles wide.
4.The (So-called) Dividing Range
In connexion with the Queensland Highlands, which form part of the Eastern Cordillera, it may be well to discuss the so-called “Great Dividing Range,” which is so prominent a feature on most maps. This belt of highlands undoubtedly constitutes the divide between the coastal drainage and that flowing westward to Lake Eyre or the Murray mouth. But, if we examine it at all closely, it is seen to be in no sense a range, but is for the most part a series of disconnected elements of very diverse origin.
In Queensland, it is only an important feature where formed of basalt flows of comparatively late date. Between these it is often a mere warp-ridge but a few hundred feet above the general level.
In the north of New South Wales the Divide is more definite for 100 miles, for here it runs along the great New England granite massif. But the Liverpool Ranges - a quite late geological formation - deviate it to the west. Here the Divide deteriorates to a mere water parting (at Cassius) between the Goulburn and Talbagar Rivers, where crustal folding, combined with the cutting action of the Goulburn, has driven the Divide far to the west. The “range” is not 2,000 feet high hereabouts.
The Divide returns along the southern rim of the Goulburn Valley towards the coast, and is then carried southwards by a series of indefinite ranges, consisting here of basalt flows, there of recent folds; and again, as at Cooma, with hardly any apparent elevation at all. Hereabouts we notice that Lake George is perched right on the Divide, while Merigan Creek flows right through the so-called Divide. Near Cooma it enters on an extraordinary zig-zag path, which points to recent interruptions in the drainage. These zig-zags around the heads of the Snowy and Tambo Rivers are almost certainly the results of important river captures. Finally, in Victoria, the great area of Pliocene basalt in the west of the State has certainly flooded pre-existing lowlands and valleys, and converted portions of them into the modern Divide.
5. The Eastern Cordillera
Lying parallel to the modern Divide, and in the north considerably to the east of it, is another belt of highlands almost coincident with the coastline These coast ranges are formed of an almost continuous series of granite masses, which reach from Tasmania to Cape York. South of Queensland the modern basalt. tapped Divide and the granite masses are mingled to a greater degree. This broad “complex” of highlands of varying origin forms a fairly well marked belt to which the name Eastern Cordillera is here applied
6. The Queensland Highlands
In the far north of this belt is one of the most interesting elevated regions in Australia. The Atherton Plateau is almost the only tropical plateau worthy of the name. No other large areas over 2,000 feet exist in our tropical areas except right on the Tropic itself at a comparatively high latitude. Furthermore, the Atherton Plateau is well-watered, fertile, and rich in minerals, and it bulks largely, therefore, in discussions of tropical settlement. Its area (over 2,000 feet) is, however, only about 15,000 square miles out of a total of 1,149,320 square miles in tropical Australia. The plateau rises gradually to the east, the summit being Mount Bartle Frere (5,438 feet), the highest point in Queensland. This mountain rises almost straight up from a narrow coastal plain. It stands right in the path of the constant trade winds, and its flanks are drenched with rains, amounting to 165 inches at Harvey Greek, This factor, combined with the recency of the uplift, has led to very rapid headward erosion by such coastal streams as the Barton, Johnstone, Mulgrave &c. The headwaters of the Mitchell, which rises right on the east coast, have accordingly been captured by the Barren River. Fine waterfalls are common, and the scenery stands out among Australian examples.
The coast has been subjected to many oscillations in recent times. A series of coastal plains of very recent origin points to an upward “joggle”. The great gorges and waterfalls also show evidence of some hundreds of feet uplift many thousand years ago. But the dominant feature is subsidence. The coral reefs of the Great Barrier probably form only a veneer of a few hundred feet on a subsided coastal margin. The festoon islands so common along the coast also clearly indicate dominant subsidence.
The Clarke Range near Mackay has only a restricted area over 2,000 feet. Some of the basalt tablelands along the Great Divide (eg., Buckland Tableland) rise to about this same level. A number of small lakes just north of the Tropic, e.g., Buchanan, Galilee, Dunn, and Mueller, seem to he relics of ancient rivers running across time present Divide. Perhaps the present Burdekin formerly drained westward into the Thomson River, via these depressions. Lake Galilee is about 20 miles long, and there is only a divide of 200 feet separating it front Belyando River.
The Darling Downs area is also largely composed of basalt. Small portions rise above 2,000 feet. The coastal rivers are shifting the divide to the west, and steep slopes flank the east of these uplands. A series of late tertiary volcanic cones constitutes the Glass House Mountains. Somewhat similar cones are found in the Peak Range farther north. Much field work remains to be done in Queensland before the topography can he adequately described, as very little investigation has been attempted away from the coastlands.
Owing to the work of David, Andrews, Sussmilch, and others, the topography of this State is fairly well known. The major divisions resemble those of Queensland. There is a low western region - not, however, in general covering artesian water as in Queensland - and a mountainous eastern division extending almost to the coastline. Several subdivisions may usefully be employed.
Broken Hill Buckle.
Riverina or Murray Basin.
B. Eastern Division (Highland)
Kosciusko and the Monaro.
Associated with the latter division are small coastal plains; such as those near the Clarence, Hunter, and Hawkesbury Rivers.
2. Western Division
(i) Lowlands. With regard to the lowland portions of the west, there is not much difference in the topography of the northern (Artesian) region and the southern (Riverina) region. Both exhibit senile valleys choked with alluvial, and so level that they merge into plains with indistinguishable divides. Thus the Paroo river in time of flood is stated to spread to a width of some 20 miles. Probably much of the alluvial is a legacy of larger rivers of the Pleistocene period. Some uplift has affected the main streams in places. Thus, at Walgett, the Darling (or Barwon) flows in a trench 30 feet below the alluvial plains. The same condition obtains at Wilcannia. The soil consists largely of black chernozem near the rivers, with much humus and unoxidized fragments of basic rocks. Older alluvial tends to be reddish arid less “sticky” owing partly to oxidization.
The southern boundary of the Artesian Division is not marked by any notable surface feature. It runs from Bourke to Dubbo near the Bogan River. On the east, the land rises rapidly to the outlying spurs of the New England Plateau. The Artesian water is found at much shallower depths than in Queensland - on an average about 1,800 feet down. (The deepest, Boronga Bore, near Mungindi, penetrates to a depth of 4,338 feet).
(ii) Central District. The central portion of New South Wales exhibits three low earth waves, which probably originated in pressure from the New Zealand area exerted on the mobile crust thrusting it against the Great Australian Shield. We have already considered the Flinders Range - the most western of these buckles. To the east lie the Broken Hill Uplands, the Cobar Peneplain, and the Blue Plateau. Those bear marks of recency and probably date from the Pleistocene or “Kosciusko” period.
(iii) The Broken Hill Upland. The Broken Hill Upland (rather inaccurately named the Barrier Ranges) consists of a horst some 100 miles long and 30 miles wide. It rises some 500 feet above the alluvial plains, which in turn are 500 feet above the sea. The upland is crossed by low ridges, which represent the edges of upturned resistant strata. Well-marked fault-scarps cut by deep gorges appear along the western edge. Large delta-fairs of an earlier wetter cycle run far out on the alluvial deposits of the Frome Plain.
(iv) The Darling River. The Darling River flows from the Northern (Artesian) Division to the Southern (Riverina) Division of the lowlands. No marked rejuvenation of the river seems to have ensued due to the buckling here, for at Wilcannia the Darling is only entrenched about 30 feet in its alluvials.
(v) The Cobar Peneplain. The Cobar Peneplain is an area some 200 miles wide of early Paleozoic rocks rising about 600 feet above the sea, and so only a little higher than the surrounding deep alluvial plains. It represents fairly closely the pre-uplift topography of most of Eastern Australia in middle tertiary times. The level area around Wyalong to the south is of somewhat the same topography.
(vi) The Riverina or Murray Basin. The Riverina Region extends from about Narrandera westwards to the border of South Australia. It is characterized by extremely level conditions, so that the rivers have the habit of delta-streams and distributaries are common. In local floods the water at times flows upstream. Billabongs and anabranches cross from river to river. Willandra Billabong in periods of flood connects the Lachlan near Hillston with the Murray at Euston. So also Yanco Creek joins the Murrumbidgee with the Murray by an alternative channel, to the south of the main drainage of the region (via Hay). Local uplift has caused the Murray to be slightly rejuvenated in its Echuca section, but very little work has been done on the topography of the Murray.
3. Eastern Division
(i) The New England Plateau. New England is the most extensive plateau in Australia, though not the highest. If covers an area about 200 miles long by 40 miles wide all over 3,000 feet high. Three bosses between Armidale and Tenterfield (Ben Lomond, Capoompeta, and Chandler’s Peak) rise to 5,000 feet, while an important high spur, called Snowy Mountain, runs to the east, and the “Barrington Tops” to the south are about the same height. Andrews writes of New England, “The conception which harmonizes must with the facts of observation appears to be that the main New England Plateau surface was developed by erosive activities near sea level, and that it has since been raised unevenly, so as to form a warped and faulted surface.” There are three of these plateau levels. The Coyra Peneplain is at about 4,300 feet elevation, the Mole Peneplain is at 4,000, the Sandon and Stannifer Peneplain at about 3,200 feet. The coastal rivers have cut back into tilts uplifted region and have formed canyons (as at the head of the Macleay) some 3,000 feet deep.
Three volcanic groups are associated with New England. The Nandewar group of trachyte cones rises to a height of 4,000 feet between Armidale and Narrabri. A similar group to the south of Narrabri is called the Warrumbungles. Its highest point is about 3,000 feet. Linking these to the main plateau is the basalt-capped highland called the Liverpool Range.
A very marked topographic feature lies just to the south of this group of highlands. It is the Cassilis Gate, and is a broad gap, well below 2,000 feet. It is the most striking break in the highlands from the latitude of Brisbane to that of Melbourne. Curiously enough, no railway so far takes advantage of this topographic advantage for a route to the west. The depression is due partly to tectonic and partly to erosional factors.
(ii) The Blue Plateau. The next massif to the south is the Blue Plateau. (The term “Blue Mountains” is a misnomer. It consists of a boldly warped portion of the crust, which has been elevated three or four thousand feet. The main flexure is along the western bank of the lower Nepean River, and here the surface rises sharply about 1,000 feet. But several other parallel folds further west bring the ancient peneplain surface to a height of over 4,000 feet at Mount Bindo (near Jenolan).
Marked faults have accompanied the folding. Near Kurrajong, a fault scarp of about 500 feet is a marked feature, and similar faults are probably common to the southward. The uplift dates back many thousand years, and marked rejuvenation and reversal of the streams is the result, It seems likely that the pre-uplift drainage here was to the north-west or north, as suggested in 1911 by the writer. Such courses are still dominant in the Wianamatta “Stillstand” (or region of negligible uplift) which lies between Sydney and the Blue Plateau. Field work being carried out at present seems to support the view that the Wollondilly and Cox Rivers originally joined the Macquarie streams to the north west. The remarkably broad and deep gorges cut in the plateau, with their unique bottle-necks, where they pass through the “hinge” of the earth fold, are due to the presence of a hard horizontal sandstone capping softer coal measures. They have been described elsewhere.
(iii) The Lake George Gate. An area of marked faulting separates the Blue Plateau from the next massif to the south. To this area of relatively low faulted topography the name of Lake George Gate has been given. Here the former tributaries of the Yass River and other streams have been ponded back by meridional faults to form lakes like Lake George (20 miles long) and Lake Bathurst. Fine “antecedent” gorges such as the Molonglo (east of Canberra) and the Murrumbidgee (as it flows west through the horst) at Burrinjack show the relative recency of the Kosciusko uplift.
(iv) Kosciusko and the Monaro. The south-east corner of New South Wales contains the highest mountains in Australia. Kosciusko rises to 7,328 feet, but it is merely the summit of a crustal block or horst with a general level of five or six thousand feet. The topography of the Kosciusko Plateau has been worked out in some detail. Glacial relics of the Pleistocene ice age, such as moraines and cirques, only occur within about 10 miles of the summit, at elevations over 5,500 feet. Sussmilch has shown that the courses of the Murrumbidgee and Snowy Rivers near Kosciusko have been largely determined by the presence of graben bounded by meridional faults.
It seems probable that a “lineament” (or line of crustal weakness) extends from Canberra southwards, perhaps to Bass Strait. The late Mr. Dannevig charted a deep submarine canyon or drowned river valley near Cape Everard, which was perhaps the southern end of this lineament. Evidences of capture are common along the courses of the Upper Murrumbidgee and of the Snowy River in this district. This lineament traverses the Monaro Plateau, which probably constitutes another crustal block parallel to the Kosciusko horst. but at a level of about 2,500 feet. It is bounded on tine east by a marked scarp, by which travellers descend rapidly to the coast. The linear and character of the coast from Cape Howe north to Bateman’s Bay indicates that faulting has played a part here. A similar coastline from the Shoalhaven northward nearly to Sydney is also probably largely determined by faulting. The term “Illawarra Range” for this faulted feature is, therefore, a misnomer and should be replaced by “Illawarra Scarp.”
The topography of Victoria may be considered in three major divisions. The Eastern Highlands are structurally associated with those of south-east New South Wales. The Northern Plains are merely portion of the Murray Basin which we have already considered. In the south-east of the State is a fairly level low area which has been termed the Great Valley of Victoria.
2. The Eastern Highlands
The marked chance in the direction of the main axis of the cordillera near Kosciusko is of much interest. Yet the Victorian highlands, like those in the south-east of New South Wales, appear also to be built up of meridional bursts arranged parallel to each other right across Victoria. The highest "blocks" are to the east, and Mounts Bogong (6,508) and Hotham (6,100) are not much lower than Kosciusko itself. The chief gap hereabouts is the Omeo “ Gate,” which separates the Victorian portion of the Kosciusko massif (with the Cobboras (6,000) and Mount Gibbo) from the Bogong Plateau. The Mitta and Tambo valleys here apparently form a "lineament" across the highlands. Lake Omeo is on this line of weakness, and the Tambo headwaters appear largely to have been captured by the Upper Mitta.
3. The Dargo High Plains
The Dargo High Plains are at about 4,500 feet elevation, and he to the south of Mount Bogong. Mount Buffalo (5,645 feet) extends to the north, raising fairly abruptly above the Murray Plains. The edges of this elevated peneplain have been deeply notched by the rivers to north and south. The Goulburn has cot a deep wide valley and has had a varied history involving several captures. Eastward the highlands are somewhat lower, hot Mounts Howitt and Wellington are over 6,000 feet. Further east again the divide becomes more ridge-like and rapidly drops from Mount Torbreck (4,995 feet) to the Kilmore "Gate," where it is only about 1,000 feet above sea-level.
The elevated portion of the State to the west of this Gate also consists of a peneplain in general sloping from Mount Macedon (3,324) to the south-west. The level is about 2,000 feet at Ballarat, 1,000 at Ararat and 600 at Hamilton. Fault scarps, similar in origin and direction to those described near Kosciusko, define the Pyrenees (3,240) and Grampians (3,827). These latter seem to be hunts above the general level of the elevated peneplain.
4. The Great Victorian VaIley
The whole of the Western Plains south of the divide (in the west) has been flooded by basalt lavas. This region between Ballarat and the Otway Ranges (of Jurassic strata some 1,900 feet high) is part of the Great Victorian Valley. It is about 500 feet above sea-level. Small volcanic cones are common throughout, such as Mount Elephant (1,294 feet), Mount Noorat, and Tower Hill. Lakes are scattered over this basalt plain, occupying depressions in the fairly lately formed surface Port Phillip would appear to he a sunken portion of the Great Valley, which, structurally, extends to the east as the Gippsland Plains. Here the Strzelecki Ranges arc of the same type and age as the Otway Ranges. On Wilson’s Promontory are isolated granite hills reaching 2,434 feet.
5. The North West Plains
The north-west of the State consists of a vast plain mostly below 500 feet and covered with alluvial deposited by the tributaries of the Murray, These latter in general end blindly in a maze of sand-hills, for the rainfall is Only 12 inches a year. The Murray has a large enough supply to flow continuously in dry years like 1914 or 1923, hut the Wimmera, Yarriambiack, and Avoca Rivers have too little catchment. Numerous swampy lakes, like Hindmarsh and Tyrrell. have developed where the tributaries end.
This State, like the adjacent region on the mainland, consists essentially of lower Paleozoic sediments buttressed by granite. But over a large portion of the centre and east a basin in the Paleozoic rocks has been filled with coal measures (ads allied deposits), and these again have been overwhelmed with basic eruptive reeks.
2. The Central Plateau
The dominant feature is the central plateau, which falls from a general level of 3,500 feet in the north-west towards the south-east, being drained by the Derwent system. This plateau seems to be a horst, the lowlands to the north and east having been relatively depressed by step faulting, which has left boll scarps (locally called tiers).
Along the western edge the plateau rises to considerable heights in Cradle Mountain (5,069), Eldon (4,789) and Frenchman’s Cap while the southern wall of the Derwent basin is crowned by Mount Field West (4,725) and Mount Wellington (4,166). The northern rim is also high (Ironstone 4,736), but the east of the plateau is much lower and connects at Oatlands (1,350) with the east coast highlands.
3. North-east and South-west Massifs
Two somewhat isolated massifa lie in the north-east and south-west respectively. The highest point in the State is Legge’s Peak (5,160) on the rectangular plateau of Ben Lomond. This is bounded on the west by the lowland drained by the Tamar and its tributaries. In the south-west of the Island, the Huon River flows parallel to the Gordon, Tamar and Derwent. These river-directions probably indicate the prevalence of lineaments across the plateaux forming Tasmania. The Wilmot and Arthur highlands in the south-west are probably outlying portions of the same uplifted peneplain. Their summits are about 3,500 feet above the sea.
4. Evidences of Late Elevation
The deep gorges of the western rivers (e.g., King, Franklin and Denison), time large lakes on the central plateau (e.g., Great Lake, Arthur and Sorell), and the truncated east coast (as at St. Mary’s where the South Esk rises on the coastal rim) are all features pointing to the comparatively late development-of the present topography of Tasmania. Moraines and other relics of the glacial age have been described as occurring on Cradle Mountain, Mount Field, Mount Anne and other peaks.
1. Australia as a Whole
Taylor - The Australian Environment. Melbourne, 1918.
Taylor - Physical Geography of Australia. Federal Handbook, 1914.
Taylor - Australian Encyclopedia, pages 954 - 928, Sydney, 5529.
2. Western Australia
Jutson - Physiography of Western Australia. Geol. Surv., Perth, 1914.
Talbot - Geology of Wiluna to Hall’s Creek. Geol. Surv., Perth, 1910.
Clark - Natural Regions of West Australia. Roy. Soc., Perth, 1926,
3. Northern Territory
Jensen - Tropical Australia. Roy. Geog. Soc., Brisbane, 1917.
Ward - Geology of Central Australia. Roy. Soc., Adelaide, 1925.
Taylor - Tropical settlement. Amer. Geog. Rev., New York, 1919.
4. South Australia
Howchin - Physiography Features. Ausn. Assoc. Adv. Sc., Melbourne 1913.
Jack - Geology of Musgrave Ranges. Geol. Surv., Adelaide, 1915.
Danes - Phyiography of N.E. Australia. Prague, 1911.
Jensen - Phyiography of Queensland. Ausn. Associates. Ad. Sc., 1923.
Jardine - Lower Fitzroy Basin. Geog. Jrl., Brisbane, 1923.
6. New South Wales
Jose, Taylor, and Woolnough - New South Wales. Christchurch, 1911.
David - Tectonic Lines of Australia. Roy. Soc., Sydney, 1911.
Andrews - Unity of Eastern Australia. Roy. Soc., Sydney, 1910.
Sussmilch - Southern tableland. Roy. Soc., Sydney, 1909.
Taylor - Eastern Australia Melbourne, 1911.
Taylor - Sydney Warped Littoral. Roy. Soc., Sydney, 1923.
Fenner - Werribee Region. Roy Soc., Melbourne, 1918.
Gregory - Victoria, Melbourne, 1903.
Wood - Tasmanian Environment. Adelaide 1923.
Lewis - Geology of Mount Anne. Royal Soc., Tasmania, 1923.
These documents will be presented in a new window.