PALEONTOLOGY. 211 



with which we are familiar; whilst, if we study the Eocene 

 fauna, the new and unknown forms which we encounter of 

 extinct species become much more frequent. On this fact 

 is based the per-centage classification of the tertiary rocks, 

 proposed by M. Deshayes and Sir C. Lyell. 



THIED LAW. The comparison of faunas of different epochs 

 that the temperature of the surface of the earth has 

 been greatly varied. 



The facts upon which this law is established are these. 

 "We find fossil animals in regions of the globe which are not 

 inhabitable by them at the present day, in consequence of 

 their low temperature, as the rhinoceros and elephant, which 

 lived under the latitude of the glacial sea. This region 

 could not, in our time, furnish a vegetation fit for the, sup- 

 port of these pachydermata. 



The fauna of the tertiary period, in Europe, presents a 

 greater analogy to the animals of the torrid than to those of 

 the temperate zone. The remains of the vegetable kingdom 

 may be cited in confirmation of this law. Europe was, 

 during the carboniferous period, covered with an immense 

 vegetation, which for luxuriance, and the character of the 

 vegetable tribes of which it was composed, can only be 

 likened to that which exists in the present inter-tropical 

 regions of the earth. 



FOURTH LAW. The species which lived, in the ancient 

 epochs had a more extended geographical distribution than the 

 species which exist in our day. 



This law has not been clearly demonstrated, nor can it 

 be definitely admitted until the numerous localities have 

 been studied, and their fossils determined with sufficient 

 accuracy. 



The observations which appear most worthy of belief tend 

 to show that we find, in contemporaneous strata, some species 

 which are common to Europe and to America. Other ob- 

 servations prove that the species which inhabited the greater 

 part of Europe, during the periods anterior to ours, had a 

 wider geographical range into the Asiatic continent and 

 boreal region, than the species which inhabit Europe at the 

 present day. 



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