xr PALEONTOLOGY AND EVOLUTION 381 



migration between the easternmost of these islands 

 and America, took place to the westward, while 

 the American side of the sea-bottom was gradually 

 upheaved, the palaeontologist of the future would 

 find, over the Pacific area, exactly such a change 

 as I am supposing to have occurred in the North- 

 Atlantic area at the close of the Mesozoic period. 

 An Australian fauna would be found underl}?ing 

 an American fauna, and the transition from the 

 one to the other would be as abrupt as that 

 between the Chalk and lower Tertiaries ; and as 

 the drainage-area of the newly formed extension 

 of the American continent gave rise to rivers and 

 lakes, the mammals mired in their mud would 

 differ from those of like deposits on the Australian 

 side, just as the Eocene mammals differ from those 

 of the Purbecks. 



How do similar reasonings apply to the other 

 great change of hfe — that which took place at the 

 end of the Palaeozoic period ? 



In the Triassic epoch, the distribution of the 

 diy land and of terrestrial vertebrate life appears 

 to have been, generally, similar to that which 

 existed in the Mesozoic epoch ; so that the Triassic 

 continents and their faunae seem to be related to the 

 Mesozoic lands and their faunae, just as those of the 

 Miocene epoch are related to those of the present 

 day. In fact, as I have recently endeavoured to 

 prove to the Society, there was an Arctogaeal con- 

 tinent and an Arctogaeal province of distribution 

 in Triassic times as there is now ; and the Saurcp- 



