GEOLOGY OF AUSTRALIA. 361 



western slope of the mountains are the Liverpool Plains, which are dotted over with 

 isolated basalt rocks. Like the regions in the north of Eui-ope, Australia also had 

 evidently its glacial epoch followed by a lacustrine period. 



In the northern section of New South Wales the water-parting gradually falls 

 in the direction of the colon}' of Queensland, where few summits attain an elevation 

 of 2,000 feet. In some districts the mountain system is even completely inter- 

 rupted, the parting line between the two slopes being formed by scarcely per- 

 ceptible undulations. But eminences exceeding 3,000 feet reappear north of 

 the tropic of Capricorn, where a granite ridge skirting the seaboard runs north- 

 westwards to the neck of York Peninsula, here merging in a small water-parting 

 of moderate elevation. 



Between the Australian Alps and the granites of North Queensland the pre- 

 vailing formations are carboniferous of various ages, some dating from paleozoic, 

 others from mesozoic times. Here also occur some granites and porphyries, and 

 on the western slopes a few volcanoes and lava fields. It is in this section of the 

 Australian highlands and on the northern slopes of the Victoria Mountains that 

 are scattered those auriferous deposits that have so greatly stimulated the develop- 

 ment of Australia. All belong to different periods of the tertiary epoch and rest 

 on a rocky bed of the Silurian system. Most of the deposits fill old fluvial channels, 

 the so-called " gutters," and in some districts they attain a thickness of over 300 

 and even 600 feet. 



West of the " backbone " of the continent the depression comprised between 

 the Gulf of Carpentaria and the Murray estuary is largely occupied with cretaceous 

 formations. From these mesozoic strata and the vast plains of tertiary origin it is 

 evident that Australia, formerly considered as the " old " continent m a pre- 

 eminent sense, has also had its revolutions, its alternating upheavals and subsi- 

 dences, like other great divisions of the globe. 



Beyond the chalk zone begin the little-known regions intersected at long 

 intervals by the itineraries of a few daring explorers. We know, however, that 

 granites and primitive rocks occur in South Australia on both sides of Spencer 

 Gulf, as well as round the margins of the saline basins in the interior. The 

 northern peninsulas facing Melville Island have also their granites and metamor- 

 phic formations. Lastly, the soutli-western regions are to a great extent consti- 

 tuted of slightly elevated granite plateaux traversed here and there by a mountain 

 range from 1,800 to 2,000 feet high. All these chains and ridges are named after 

 the earl}' explorers or statesmen distinguished in contemporary politics. The 

 MacDouall group, lying east of the overland telegraph line, abounds in precious 

 stones, some of which have been doubtfully or wrongly described as " rubies," 



The " desert sandstone," comprising over one- third of Australia, is probably 

 of more recent origin than any of the continental mountain systems. But owing 

 to the general absence of fossils its age cannot be accurately determined, although 

 the upheaval of the plateaux, hills, and plains in this arid wilderness is by most 

 geologists referred to pliocene times. In North Queensland it overlies cretaceous 

 formations. Its numerous depressions have been produced by meteoric agencies. 



