BY H. I. JENSEN 493 



present day. He discountenanced particularly the ideas of 

 gigantic cataclysms and deluges such as were imagined by earlier 

 geologists to account for their observations. 



Although Lyell's view is correct in a general sense, it becomes 

 more and more apparent from a study of geology that there have 

 been periods of comparative quiet and periods of intense distur- 

 bance in the history of our planet. This fact is admitted by 

 Chamberlin and Salisbury in their ' Geology,' Vol. i., p. 572. 



Joseph Barrell* has shown that the early Cambrian, all over 

 the earth's surface, was a period of great continental extension 

 and uplift. During the Eopalseozoic (Cambrian, Silurian and 

 Devonian), the continents again became largely resubmerged. 

 These were periods of comparative quiet. In late Devonian and 

 early Carboniferous times there were again great epeirogenic 

 uplifts, but in late Carboniferous times subsidence predominated. 

 The Permian and early Triassic were periods of elevation, 

 whereas the Jurassic, Cretaceous, and Eocene were eras of sub- 

 sidence in which many continents were worn down and partly 

 submerged. In the middle Tertiary again great uplifts took 

 place. 



In a general sense this statement holds true, yet there were 

 numerous exceptions. It is not hard to find some area of limited 

 extent, the Sydney basin for instance, which subsided during 

 the Permian and Triassic and underwent elevation during the 

 Cretaceous and Eocene. 



Just as we meet with periods of continental extension and 

 periods of gradual submergence, so too we find that there have 

 been periods of intense vulcanicity and of comparative quiet. 

 In general, the volcanic epochs agree closely with the transition 

 periods which ushered in the periods of continental extension 

 and uplift. Thus, in every part of the world we find that the 

 late Carboniferous and early Permian were remarkable for 

 intense vulcanicity. In Australia great lava-flows and mighty 

 granitic intrusions are assigned to these times; for example, in 

 New South Wales we have the great granitic intrusions of the 



* Journal of Geology, Vol.xiv. No. 5, July- August, 1906. 



