Page:Handbook of Western Australia.djvu/28

16 and limestones, the greatest thickness of which does not probably in any place exceed 700 feet. These form flat-topped ranges, and by process of denudation and consequent separation from the mass, detached masses and peaked hills, which are characteristic features of the country over a large portion of its area. The arenaceous and cretaceous deposits have, in process of denudation, been cut into valleys and gullies, in the courses of which the base rock is commonly laid bare; but as these deposits, even when obviously similar in formation, are found at different elevations, and as science has recently confirmed the possibility of similar deposits having been made at different periods under similar conditions, it will not follow that these are all of the same period in time, or that they have even been continuous. On the contrary, it would seem that the different positions in which such deposits are found are due to gradual or successive elevations of the land from its Western Coast, but, in addition to these causes of the superficial formation, recent examination of the Southern district of the Colony has shown that its area has been traversed by elevations of eruptive rocks. The same features have been observed in the upper basins of the Murchison River, and the highest and most prominent hills and ranges throughout the country have been so formed; those on the South being granitic or schistose, while those to the North are described as basaltic, trappean, or volcanic. Those erupted rocks, both on the South and in the Murchison District, form well defined ranges culminating in bold rocky peaks trending from East and North to South and West, and, about the sources of the Murchison, divide a series of parallel valleys forming the basins of its affluents. True basalt has been found in its crystalline forms in the South Western angle of the Colony at Bunbury on the