EVIDENCE FROM PALEONTOLOGY 93 



close study of the genealogy of some restricted 

 group. 



It has often been objected that the palaeontological 

 record, as we actually have it, is irreconcilable with 

 the evolutionary conception, because of the many 

 cases of the sudden and unheralded appearance of 

 new kinds of organisms, such as the remarkable 

 outburst of modern types of plants and fishes in 

 the upper Cretaceous period. This objection over- 

 looks the phenomena of migration, the importance 

 of which has only lately come to be recognized; the 

 many geographical changes in the connections be- 

 tween the different continents and between the 

 seas, which have demonstrably occurred in the 

 past, have from time to time altered the possibilities 

 and directions of migration. Hence, the appear- 

 ance in any given area of new forms may either be 

 through the modification of older forms which pre- 

 viously inhabited that area, or by immigration from 

 some other region. It is therefore not to be taken 

 for granted that any group originated in the region 

 where we happen first to find it; quite as frequently 

 it arose in some other region and spread gradually 

 from that. A very instructive illustration of this 

 principle is afforded by the history of the elephants, 

 which appeared suddenly (lower Miocene) in Europe 

 and somewhat later (middle Miocene) in North 

 America. In neither continent has anything been 

 found in any preceding formation, which could plausi- 

 bly be regarded as ancestral to these ancient and 



