THE PRE-ADAMITE EARTH. 



the media in which animals existed, whether it be air or water, 

 have remained the same both on land and sea. 



Fourthly. The media of existence being always the same, no 

 change in these media can be Adduced as a cause for the succes- 

 sive extinctions and reproductions of the fauna of the earth, 

 which have been manifested by geological phenomena as taking 

 place during the successive geological periods, a conclusion of 

 immense importance in the history of the globe. 



Fifthly. All the researches which have been made in the fossil 

 fauna, deposited in the strata of the earth, lead to a conclu- 

 sion of high geological importance, that, until the epoch which 

 immediately preceded the appearance of the human race and its 

 contemporaneous tribes upon the globe, all that part of the earth 

 which has undergone a close and accurate geological survey, 

 including France, England, Germany, Italy, Switzerland, Spain, 

 Portugal, part of Russia, and the adjacent seas, were inhabited by 

 a fauna altogether tropical, and such as is at present found only 

 under the torrid zone. We are forced, therefore, to the conclusion 

 that, until the present period, the isothermal zones now observed 

 had no existence. 



550. Of 1473 fossil genera hitherto discovered, 16 only are found 

 to exist in all the stages without exception. The remaining 1457 

 are distributed in different proportions throughout the stages. 

 In some cases it is seen that certain genera are only found in a 

 single stage ; in others they prevail in two stages ; in others in 

 three or more ; but, save in rare and exceptional cases, when 

 they prevail in two or more stages, these stages are in regular 

 geological succession. This persistence of the genera is a very 

 important geological and paleeontological fact. The exceptions to 

 it do not exceed 3 per cent, of the entire number of fossil genera, 

 and may, therefore, be regarded as arising from some accidental 

 cause. 



551. This peculiar distribution of generic forms of the 

 fossils, supplies to the geologist most useful stratigraphical 

 tests. Thus, if a genus known to exist only in one peculiar 

 geological stage, be found in any part of the crust of the earth 

 whose structure has not been previously well ascertained, its 

 presence may be taken as a certain indication of the character 

 and position of the stage in which it is deposited. 



The Contemporaneous Age. 



HUMAN PERIOD. 



552. The disruption of the -earth's crust, extending W. 16 S., 

 and E. 16 N., through which the chain of the great Alps was 



152 



