496 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



1. Azoic. — In the Pre-Cambrian arid Archaean eras great vol- 

 canic activity prevailed. The Kosciusko and Gippsland muscovite 

 granites and gneisses and corresponding rocks in Tasmania, the 

 fundamental granites of the Cobar massive, and many other 

 masses now for the most part obscured by later sediments, were 

 intruded at this time. Similar rocks underlie the Cretaceous of 

 South Australia and Western Queensland, and extend over large 

 areas in Western Australia. 



The igneous rocks of this period comprise both acid and basic 

 varieties, and both deep-seated and extrusive types. The basalt 

 of the Antrim plateau, near Kimberley, in Western Australia, 

 is one of the few examples of basic lava of very great antiquity. 



The volanic rocks of this period are, as far as known at present, 

 never alkaline. 



2. PaLjEOPYrogenic. — In this period occurred the intrusions 

 of biotite granite of Mount Kosciusko and of the Alpine pro- 

 vinces of Victoria; the Bathurst and Hartley Vale granites with 

 sphene; the elvan or quartz-prophyry of Mount Bischoff, Tas- 

 mania; other Tasmanian granites; the Victorian grano-diorites; 

 the Moonbi granites, Tamworth tuffs and the Snowy River 

 porphyries of New South Wales, &c, &c. 



3. Mesopyrogenic. — During early Devonian times a narrow 

 belt along the east coast of Australia was undergoing heavy 

 sedimentation, evidence of which we see in the Shoalhaven dis- 

 trict Devonian series, the New EnglandC?) and Tamworth districts, 

 and in the coastal ranges of Queensland, yet most of the con- 

 tinent was being slowly elevated. During late Devonian and 

 Carboniferous times practically the whole of New South Wales 

 was undergoing broad uplift and erosion. This was also the 

 case with Queensland west of the Dividing Range, but consider- 

 able stretches of the east coast of the northern State were at the 

 same time undergoing gradual subsidence and sedimentation. 

 This latter movement was particularly marked in the Burdekin 

 area.* By the end of the Carboniferous many land-masses 



* Jack and Etheridge, Geology and Palaeontology of Queensland; T. W. E. 

 David, Presidential Address to the Linnean Society of New South Wales, 

 Proceedings, 1893, p.571. 



