378 DARWINISM chap. 



found in a space 300 paces long by 60 paces broad, many of 

 the species existing in enormous quantities. 



The Pikermi fossils belong to the Upper Miocene forma- 

 tion, but an equally rich deposit of Upper Eocene age has 

 been discovered in South- Western France at Quercy, where M. 

 Filhol has determined the presence of no less than forty-two 

 species of beasts of prey alone. Equally remarkable are the 

 various discoveries of mammalian fossils in North America, 

 especially in the old lake bottoms now forming what are 

 called the " bad lands " of Dakota and Nebraska, belonging to 

 the Miocene period. Here are found an enormous assemblage 

 of remains, often perfect skeletons, of herbivora and carnivora, 

 as varied and interesting as those from the localities akeady 

 referred to in Europe ; but altogether distinct, and far ex- 

 ceeding, in number and variety of species of the larger animals, 

 the whole existing fauna of North America. Very similar 

 phenomena occiu" in South America and in Australia, leading 

 us to the conclusion that the earth at the present time is 

 impoverished as regards the larger animals, and that at each 

 successive period of Tertiary time, at all events, it contained 

 a far greater number of species than now inhabit it. The 

 very richness and abundance of the remains which we find 

 in limited areas, serve to convince us how imperfect and 

 fragmentary must be our knowledge of the earth's fauna at 

 any one past epoch ; since we cannot believe that all, or 

 nearly all, of the animals which inhabited any district were 

 entombed in a single lake, or overwhelmed by the floods of a 

 single river. 



But the spots where such rich deposits occur are ex- 

 ceedingly few and far between when compared "with the vast 

 ! areas of continental land, and we have every reason to believe 

 that in past ages, as now, numbers of curious species were 

 rare or local, the commoner and more abundant species giA'ing 

 a very imperfect idea of the existing series of animal forms. 

 ' Yet more important, as sho'vving the imperfection of om' 

 knowledge, is the enormous lapse of time between the several 

 formations in which we find organic remains in any abundance, 

 so vast that in many cases we find ourselves almost in a new 

 world, all the species and most of the genera of the higher 

 animals having undergone a complete change. 



