THE GEOLOGICAL HISTORY OF THE COLONY 439 



the polar temperatures. Profs. Chamberlin and Salis- 

 bury l have made a brilliant attempt to work out these 

 hypotheses, and support them by geological evidence 

 which is worth serious consideration. Their theory 

 cannot be fully summarised here, but it depends chiefly 

 on the effect of the formation of thick and extensive 

 limestones in Carboniferous times in removing carbon 

 dioxide from the air faster than it was renewed, a pro- 

 cess which was continued in Permian times by the 

 weathering of rocks on the supposed much greater land 

 areas of that period ; this extension of the land at the 

 expense of the ocean is, in its turn, supposed to have 

 brought about oceanic and atmospheric circulations 

 conducive to cold climatic conditions in the areas known 

 to have been covered with ice and snow. 



There seems to have been in late Palaeozoic times a 

 great mass of land, whose boundaries are very imper- 

 fectly known, but which included part of Africa to the 

 north of the Colony, a part of Australia, Eastern South 

 America and a part of India, and which stretched across 

 the Atlantic and Indian Oceans; on this land glacial 

 conditions prevailed during a certain period. The flora 

 and fauna of the land during and subsequent to the cold 

 period were quite different to those which spread over 

 the European and North American areas at the same 



1 Geology, vol. ii., pp. 655-77, London, 1906. For other discussions 

 of this question see papers by T. W. E. David, and J. W. Gregory, Con- 

 gres Geolog. Internal., 1906, Mexico. A. Penck, Zeitschr. d. Gesellsch.f. 

 Erdkunde zu Berlin, xxxv., 1901, p. 239 ; E. Koken, N. J. fiir Min., 

 etc., Festband, 1907, p. 530. E. Philippi, Centralblatt fiir Min., etc., 

 1908, p. 353. (An excellent general account of the Dwyka by this geologist 

 is to be found in Zeitsch. der Deutsch. Geol. Gesellsch., 1904, p. 304.) 



