Page:EB1911 - Volume 28.djvu/54

Rh The Tambo (120 m. long), which rises in the heart of the Australian Alps, crosses the Gippsland plains and falls into Lake King, one of the Gippsland lakes; into the same lake falls the Mitchell river, rising also in the Australian Alps. The Mitchell is navigated for a short distance. The Latrobe empties itself into Lake Wellington after a course of 135 m.; it rises at Mount Baw Baw. The Yarra Yarra rises in the “Black Spur” of the Australian Alps. Emerging in a deep valley from the ranges, it follows a sinuous course through the undulating plains called the “Yarra Flats,” which are wholly enclosed by hills, on whose slopes are some of the best vineyards of Australia; it finds its way out of the Flats between high and precipitous but well-wooded banks, and finally reaches Port Phillip Bay below Melbourne. Owing to its numerous windings its course through that city and its suburbs is at least thirty miles. Nearer to the sea its waterway, formerly available for vessels drawing 16 ft., has now been deepened so as to be available for vessels drawing 20 ft. The Barwon, farther west, is a river of considerable length but little volume, flowing chiefly through pastoral lands. The Hopkins and Glenelg (280 m.) both water the splendid pastoral lands of the west, the lower course of the former passing through the fertile district of Warrnambool, well known throughout Australia as a potato-growing region.

In the west there are Lakes Corangamite and Colac, due north of Cape Otway. The former is intensely salt; the latter is fresh, having an outlet for its waters. Lakes Tyrrell and Hindmarsh lie in the plains of the north-west. In summer they are dried up, and in winter are again formed, by the waters of rivers that have no outlet. In the east are the Gippsland lakes, formed by the waters of the Latrobe, Mitchell and Tambo, being dammed back by the sand hills of the Ninety Mile Beach. They are connected with Bass Strait by a narrow and shifting channel through a shallow bar; the government of Victoria has done a great deal of late years to deepen the entrance and make it safer. The upper lake is called Lake Wellington; a narrow passage leads into Lake Victoria, which is joined to a wider expanse called Lake King. These are all fresh-water lakes and are visited by tourists, being readily accessible from Melbourne.

Geology.—Victoria includes a more varied and complete geological sequence than any other area of equal size in Australia. Its geological foundation consists of a band of Archean and Lower Palaeozoic rocks, which forms the backbone of the state. The sedimentary rocks in this foundation have been thrown into folds, of which the axes trend approximately north and south. The Lower Palaeozoic and Archean rocks build up the Highlands of Victoria, which occupy the whole width of the state at its eastern end, extending from the New South Wales border on the north to the shore of the Southern Ocean on the south. These Highlands constitute the whole of the mountainous country of Gippsland and the north-eastern districts. They become narrower to the west, and finally, beyond the old plateau of Dundas, disappear beneath the recent loams of the plains along the South Australian border. The Lower Palaeozoic and Archean rocks bear upon their surface some Upper Palaeozoic rocks, which occur in belts running north and south, and have been preserved by in folding or faulting; such are the Grampian Sandstones in the west; the Cathedral Mountain Sandstones to the north-east of Melbourne; the belt of Devonian and Lower Carboniferous rocks that extends across eastern Victoria, through Mount Wellington to Mansfield; and finally, far to the east, is the belt of the Snowy river porphyries, erupted by a chain of Lower Devonian volcanoes. Further Upper Palaeozoic rocks and the Upper Carboniferous glacial beds occur in basins on both northern and southern flanks of the Highlands. The Mesozoic rocks are confined to southern Victoria; they build up the hills of southern Gippsland and the Otway Ranges; and farther west, hidden by later rocks, they occur under the coast of the western district. Between the southern mountain chain and the Victorian Highlands occurs the Great Valley of Victoria, occupied by sedimentary and volcanic rocks of Kainozoic age. The North-Western Plains, occurring between the northern foot of the Highlands and the Murray, are occupied by Kainozoic sediments.

Victoria has a fairly complete geological sequence, though it is poorer than New South Wales in the Upper Carboniferous and Lower Mesozoic. The Archean rocks form two blocks of gneisses and schists, which build up the Highlands of Dundas in the west, and of the north-eastern part of Victoria. They were originally described as metamorphosed Silurian rocks, but must be of Archean age. Another series of Archean rocks is more widely developed, and forms the old framework upon which the geology of Victoria has been built up. They are known as the Heathcotian series, and consist of phyllites, schists and amphibolites; while their most characteristic feature is the constant association of foliated diabase and beds of jasperoids. Volcanic agglomerates occur in the series at the typical locality of Heathcote. The Heathcotian rocks form the Colbinabbin Range, which runs for 40 m. northward and southward, east of Bendigo. They are also exposed on the surface at the eastern foot of the Grampian Range, and at Dookie, and on the southern coast in Waratah Bay; they have been proved by bores under Rushworth, and they apparently underlie parts of the Gippsland coalfields. The Cambrian rocks have so far only been definitely proved near Mansfield. Mr A. M. Howitt has there collected some fragmentary remains of Olenellus and worm tubes of the Cambrian genus Salterella. These beds at Mansfield contain phosphatic limestones and wavellite.

The Ordovician system is well developed. It consists of slates and quartzites; and some schists around the granites of the western district, and in the Pyrenees, are regarded as metamorphic Ordovician. The Ordovician has a rich graptolitic fauna, and they have been classified into the following divisions:— The Ordovician beds are best developed in a band running north-north-west and south-south-east across Victoria, of which the eastern boundary passes through Melbourne. This Ordovician band begins on the south with the block forming the plateau of Arthur's Seat and Mornington Peninsula, as proved by Ferguson. This outlier is bounded to the north by the depression of Port Phillip and the basalt plains west of Melbourne. It reappears north of them at Lancefield, whence it extends along the Highlands, past Ballarat, with southern outliers as far as Steiglitz. It forms the whole of the Ballarat Plateau, and is continued northward through the goldfields of Castlemaine, Bendigo and the Pyrenees, till it dips under the North-Western Plains. Certain evidence as to the age of the rocks in the Pyrenees has not yet been collected, and they may be pre-Ordovician. Some Upper Ordovician rocks occur in the mountains of eastern Gippsland, as near Woods Point, and in north-eastern Victoria, in Wombat Creek.

The Silurian system consists of two divisions: the lower or Melbournian, and the upper or Yeringian. Both consist in the main of sandstones, quartzite's and shales; but the upper series includes lenticular masses of limestone, at Lillydale, Loyola and along the Thomson river. The limestones are rich in typical Silurian corals and bryozoa, and the shales and sandstones contain brachiopods and trilobites. The Silurian rocks are well exposed in sections near Melbourne; they occur in a belt running from the southern coast at Waratah Bay, west of Wilson's Promontory, north-north-westward across Victoria, and parallel to the Ordovician belt, which underlies them on the west. The Silurian rocks include the goldfields of the Upper Yarra, Woods Point, Walhalla and Rushworth, while the limestones are worked for lime at Lillydale and Waratah Bay. The Devonian system includes representatives of the lower, middle and upper series. The Lower Devonian series includes the porphyries and their associated igneous rocks, along the valley of the Snowy river. They represent the remains of an old chain of volcanoes which once extended north and south across Victoria. The Middle Devonian is mainly formed of marine sandstones, and limestones in eastern Gippsland. It is best developed in the valleys of the Mitchell, the Tambo and the Snowy rivers. The Upper Devonian rocks include sandstones, shales and coarse conglomerates. At the close of Middle Devonian times there were intense crustal disturbances, and the granitic massifs, which formed the primitive mountain axis of Victoria, were then intruded.

The Carboniferous system begins with the Avon river sandstones, containing Lepidodendron, and the red sandstones, with Lower Carboniferous fish, collected by Mr Geo. Sweet near Mansfield. Probably the Grampian Sandstone, the Cathedral Mountain Sandstone, and some in the Mount Wellington district belong to the same period. The Upper Carboniferous includes the famous glacial deposits and boulder clays, by which the occurrence of a Carboniferous glaciation in the Southern Hemisphere was first demonstrated. These beds occur at Heathcote, Bendigo, the Loddon Valley, southern Gippsland and the North-Eastern district. The beds comprise boulder clay, containing ice-scratched boulders, and sometimes rest upon ice-scratched, moutonne surfaces, and some lake deposits, similar to those laid down in glacial lakes. The glacial beds are overlain by sandstones containing Gangamopteris, and Kitson's work in Northern Tasmania leaves no doubt that they are on the horizon of the Greta or Lower Coal Measures of New South Wales.

The Mesozoic group is represented only by Jurassic rocks, which form the mountains of southern Gippsland and include its coalfields. The rocks contain fossil land plants, occasional fish remains and the claw of a dinosaur, &c. The coal is of excellent quality. The mudstones, which form the main bulk of this series, are largely composed of volcanic debris, which decomposes to a fertile soil. These rocks trend south-westward along the Bass Range, which reaches Western Port. They skirt the Mornington Peninsula, underlie part of Port Phillip and the Bellarine Peninsula, and are exposed in the Barrabool Hills to the south-west of Geelong; thence they extend into the Otway Ranges, which are wholly built of these rocks and contain some coal seams. Farther west they disappear below the recent sediments and volcanic rocks of the Warrnambool district. They are exposed again in the Portland Peninsula, and rise again to form the Wannon Hills, to the south of Dundas.

The Kainozoic beds include three main series: lacustrine, marine and volcanic. The main lacustrine series is probably of Oligocene