Page:EB1911 - Volume 19.djvu/561

 Kiama, Shoalhaven, Bateman’s Bay, Ulladulla, Merimbula, and Twofold Bay. North of Sydney the secondary ports are at the mouths of the Hawkesbury, Manning, Hastings, Macleay, Nambucca, Bellingen, Clarence, Richmond and Tweed rivers. The rivers of the sea-board are as just enumerated, the only other of importance being the Hunter. The Richmond drains an area of 2400 sq. m. and is navigable for 60 m. The Clarence is a fine stream draining an area of 8000 sq. m.; it has a course of 240 m. navigable for 67 m. The Macleay drains an area of 4800 sq. m., and empties at Trial Bay after a course of 200 m., of which 20 m. are navigable. The Hastings and Manning are both important rivers. The Hunter is one of the chief rivers of the state and embouches at Port Hunter or Newcastle Harbour after a course of 200 m. It drains an area of 11,000 sq. m., more than twice the area of the Thames basin. Less commercially important than the Hunter, the Hawkesbury is nevertheless a fine stream; it has a course of 330 m., of which 70 m. are navigable. South of Sydney the rivers are of less importance; the principal is the Shoalhaven, 260 m. long, draining an area of 3300 sq. m.

Climate.—The three geographical regions above described constitute three distinct climatic divisions. The coastal region, 28° to 37° S. lat., shows a difference between the average summer and winter temperatures of only 24° Fahrenheit. Sydney, which is situated midway between the extreme points of the state (33° 51′ S.), has a mean temperature of 63°, the mean summer temperature being 71° and that of winter 54°, showing a mean range of 17°; the highest temperature in the shade experienced at Sydney in 1896 was 108·5°, and the lowest 35·9. The coastal district has an area of 38,000 sq. m., over which there is an average rainfall of 42 in. The rainfall is greatest at the sea-board, diminishing inland; the fall also diminishes from north to south. Sydney has an average fall of 50 in., while the Clarence Heads, in the north, has 58 in., and Eden, in the south, 35·5 in. The tableland is a distinct climatic region. On the high southern plateau, at an elevation of 4640 ft., stands the town of Kiandra, with a mean summer temperature of 56·4° and winter of 32·5°. Cooma, in the centre of the Monaro plains, at an elevation of 2637 ft., has a mean summer temperature of 65·9° and winter, 41·7°; its summers are therefore as mild as those of London or Paris, while its winters are much less severe. On the New England tableland, under latitude 30° S., the yearly average temperature is 56·5°, the mean summer 67·7° and the mean winter 44·3°. The tablelands cover an area of 85,000 sq. m. and have an average rainfall of 32·6 in.; there is, however, a small area in the southern portion where an average fall of 64 in. is experienced. In the western division, or great plains, severe heat is experienced throughout the summer, and on occasional days the thermometer in the shade ranges above 100° Fahrenheit, but it is a dry heat and more easily borne than a much less degree of temperature at the sea-board. The mean summer temperature ranges between 75° at Deniliquin in the south and 84° at Bourke. The mean range in winter is between 48° and 54·5°, and, accompanied as this is with clear skies, the season is very refreshing. West of the tableland the amount of rainfall decreases as the distance from the Pacific increases, and in a large area west of the Darling the average annual rainfall does not exceed 10 in. For the whole western division, embracing an area of 188,000 sq. m., the average rainfall is 19·8 in.

Geology.—New South Wales consists geologically as well as geographically of three main divisions which traverse the state from north to south. The highlands of eastern Australia form the middle belt of the state, to the east of which are the low coastal districts and to the west the wide western plains. The highlands of New South Wales consist, geographically, of a series of tablelands, now in the condition of dissected peneplains; geologically, they are built of a foundation of Archean and folded Lower Palaeozoic rocks, covered in places by sheets of more horizontal Upper Palaeozoic and Mesozoic rocks; these deposits occur along the edge of the highlands, and are widely distributed on the floor of the coastal districts. They have been lowered to this level by a monoclinal fold, which has brought down the Mesozoic rocks, so that they extend eastward to the coast, where they dip beneath the sea. The western plains contain isolated ridges of the old Archean and Lower Palaeozoic rocks; but in the main, they consist of plains of Cretaceous beds covered by Cainozoic drifts. The stratified rocks in the highlands strike north and south, as if they had been crumpled into folds, in Upper Palaeozoic times, by pressure from east to west. The weak areas in the crust caused by the earth movements were invaded by great masses of Devonian granites. They altered the Lower Palaeozoic rocks on their edges, and were once thought to have converted wide areas of Lower Palaeozoic rocks into schists and gneisses. Most of these foliated rocks, however, are doubtless of Archean age. The highland rocks no doubt once extended along the whole length of the state from north to south; but they are now crossed by a band of Upper Palaeozoic sediments, which extend up to the valley of the Hunter river and separate the Blue Mountains and the Southern Highlands of New South Wales from the New England tableland to the north.

The oldest rocks in New South Wales are referrable to the Archean system, and consist of gneisses and schists, including the glaucophane-schists in the New England tableland, and hornblende-schists of Berthong. The Archean rocks are comparatively sparsely exposed in New South Wales. They enter the state from the south, being continuous with the Archean block of north-eastern Victoria. They occupy a large area in the western districts of New South Wales, where a projection from the Archean plateau of central Australia crosses into the state from South Australia; it is best exposed in the Barrier Ranges around Broken Hill. Cambrian rocks have not yet been discovered in New South Wales; but Pittman has recorded an Agnostus from Mandurama, near Orange. The rocks of the Ordovician system, though widely distributed, have not always been separated from the Silurian rocks, which they often closely resemble lithologically. The occurrence of Ordovician rocks was first established by Dun at Tomingley, 33 m. S.W. of Dubbo, where he discovered graptolites that he identified as Climacograptus and Dicellograptus. Other graptolites have been found near Orange, and at Lyndhurst, near Carcoar. The fossiliferous horizon is of Upper Ordovician age. The extent of the Ordovician will probably be increased by addition of areas, which cannot yet be separated from the Silurian. The Silurian system is the best-known constituent of the Lower Palaeozoic foundation of New South Wales. The rocks consist of sandstones, quartzites, slates and shales, associated with lenticular masses of limestone. The typical Silurian rocks are richly fossiliferous, the shales containing trilobites, the sandstones many brachiopods, and the limestones a rich coral and bryozoan fauna. There are also beds of chert, which are largely composed of radiolaria. Caves have been dissolved in the limestones by underground streams; the jenolan caves in the Blue Mountains and those of Yarrangobilly and the Goulburn district are the most famous. The slates of the Silurian have been bent into folds, and saddle reefs occur along the axis of the folds, as at Hargraves. Numerous quartz reefs occur both in the Silurian and Ordovician rocks. In these reefs the chief mineral is gold. Some schists, attributed to the Silurian, but possibly older, contain platinum; and associated with the limestones are beds of copper.

The rocks of the Devonian system rest unconformably upon the Silurian; but some beds of which the age is still uncertain are called Devono-Silurian. The Devonian beds are well developed in the Blue Mountains, where the lower Devonian sediments at Mount Lambie are estimated to be 10,000 ft. in thickness. They are extensively developed along the Cox river and along the slopes of Mount Canoblas. They are also developed in the New South Wales highlands, to the south-east of Goulburn. Some of the best-known exposures are in the ranges which rise above the western plains, such as the Rankin Range on the Darling and the Kokopara Range to the north of the Murrumbidgee. The Devonian rocks at Yalwal are sharply folded and are associated with a series of rhyolites and basic lavas. The lower part of this series is probably Lower Devonian; and it is covered by shales and volcanic rocks belonging to the Upper Devonian. In the extreme south-east of New South Wales, at the head of the Genoa river, are sandstones with Archaeopteris howitti, which are an extension of the Lower Devonian beds of Victoria; while farther to the east, at Eden and Twofold Bay, are Upper Devonian sandstones.

The Devonian system is separated from the Carboniferous by an interval, during which there were powerful earth movements; they produced a lofty mountain chain, running north and south across New South Wales. The highlands are the worn down stumps of this mountain line. In Lower Carboniferous times these mountains were snow-capped, and the valleys on their flanks were occupied by glaciers.

The Lower Carboniferous beds are represented by conglomerates and sandstones with some shales and limestones. The sandstones are characterized by Lepidodendron (Bergeria) australe. It is associated with beds of lava and volcanic ash, some of which contain copper ores. Granites and granodiorites were intruded at this period into the older rocks, and altered the adjacent Devonian beds into slates and quartzites, and formed gold-quartz veins, which have been worked in the Devonian rocks at Yalwal. The Lower Carboniferous rocks also occur in the Blue Mountains along the Cox river and Capertee river; and a northern continuation occurs along the western slope of the New England tableland, from the Macintyre river to the Queensland border.

The Upper Carboniferous rocks are most important from their rich seams of coal. They occupy from 24,000 to 28,000 sq. m., which are best exposed in the Hunter river and around Newcastle.