Topography and its Effect on Climate.
A contour map of Australia shows that the continent is strikingly devoid of strong contrasts. Three-quarters of the land mass lies between the 600 and 1,500 feet contours in the form of a huge plateau. Of the remainder, there is a low-lying area comprising the Murray and Lake Eyre Basins, partly separated by the Flinders and Barrier Ranges, and, secondly, a fringe of land with an elevation of 2,000 or 3,000 feet, culminating in 7,000 feet at Mt. Kosciusko, extending through Victoria, Eastern New South Wales, and Eastern Queensland. Isolated elevated areas such as the MacDonnell and Musgrave Ranges in Central Australia, and others in Ashburton, Kimberley, Arnhem Land reach 3,000 or 4,000 feet, but are usually of the nature of bulges on the surface of the plateau rather than true mountain ranges.
Surrounding the central dry area of Australia, the isohyets describe almost concentric curves, any modifications being almost entirely due to variations in elevation. Thus, the Darling Ranges to a great degree account for the excellent rainfall of the south-west corner of Australia. The Flinders Range (South Australia) and Australian Alps in the south-east have heavier rainfalls than the surrounding tracts owing to their cooling effect on the air currents. Along the eastern elevated margin of Australia every ridge between large river valleys accounts for a somewhat greater rainfall. Examples of the latter type are the Peak Range and Darling Downs in Queensland. Where the eastern ranges of Northern Queensland (Bellenden Ker, 5,000 feet) obstruct the South-east Trade Winds, there occurs the heaviest rainfall (165.58 inches) in Australia. In Western Tasmania there is a superfluity of rain for similar reasons, though here, the constant "stormy westerlies" play the part of water bearers.
A brief notice may be devoted to the south-east corner of Australia where, in only 15 per cent. of the total area, no less than 85 per cent. of the population of the continent dwells. Here the contours have been very approximately charted and the occurrence of alternating areas of a drier and wetter type than normal is a very interesting and marked feature. In the map shown on Fig. 56, it will be noticed that the so-called Dividing Range in the south consists really of five or six more or less disconnected "massifs." In the north is the largest of all—The New England Plateau. Then a broad low gap (near Cassilis), of much physiographic importance, and hence specially named a Geocol, separates the first massif from the Blue Mountain massif. Another geocol around Lake George is the northern boundary of two well-marked mountain areas. These latter—the Snowy and Tindery Ranges—are separated by a long north-south fault valley, or subsidence area, which has been named the Australian Rift Valley, with its summit at the Cooma Geocol.
The Snowy Mountains continue as the Bowen Mountains in Victoria, and are separated from the more eastern massif (the Barry Mountains) by the Omeo Geocol. At Kilmore the cordillera practically finishes, though a well-marked low plateau near Ballarat prolongs the main divide to the westward.
If we now consider the distribution of rainfall, we shall recognise how closely it is bound up with this alternation of a highland and geocol.
