164 ANTARCTIC CONTINENT. [CH. Ill 



necessitated by alterations in the physical condition of the 

 environs, commenced, a fauna with an earlier facies has 

 been imposed upon a later one, as the Devonian of Britain 

 upon the Carboniferous of Africa, or the American Silurian 

 upon the British Devonian ? " The migration of one 

 animal might have been in one direction and the migra- 

 tion of another in the reverse direction. 



Besides the migration of animals can hardly be sup- 

 posed always or often to occupy a space of time that 

 could be fairly compared to a geological period. Especially 

 is this the case with marine creatures whose powers of dis- 

 persal are so much greater than those of terrestrial animals. 

 The Indo-Pacific fauna for example is widely spread at 

 the present day ; and formations now being laid down at 

 the extremities of this vast area are not only synchronous 

 but will entomb the remains of largely similar organisms, 

 often of identical species. 



These general considerations lead to the discussion of 

 the following particular examples of a possibly greater ex- 

 tension of land in past times through what is now deep sea. 



Evidence in favour of a formerly more extensive 



Antarctic Continent. 



Faunal conditions in the southern hemisphere have 

 recently been applied again to the question of a former 

 northward extension of the antarctic continent. The 

 evidence has been brought together by Mr H. O. Forbes 1 . 



1 Proc. Roy. Geog. Soc. 1894. 



