THE IIU.MAX SPECIES. 103 



first, having no physical instrumentality, is liable to be con- 

 tracted to within assumed chronological data, commencing at 

 arbitrary epochs, not supported by researches in geology, and 

 often appearing to be of insufficient duration ; while the second, 

 being based upon measures of length, either undefined, or vary- 

 ing in different places and times, are, from an innate propensity 

 in the human mind to magnify the unknown, stated to be more 

 than the reality. The purpose before us is, however, sufficiently 

 attained, by taking given ages for the one, and approximation 

 to true distances for the other. We can, by these means, 

 notice a succession of epochs in the conditions of the earth's 

 surface, each adapted to the existence of vertebrated animals, 

 with, it appears, an atmospheric state, gradually more suited 

 for mammalia, of certain orders and families, until it became 

 fit for the reception of man, whose creation may have synchro- 

 nized with the decay and subsequent disappearance of a great 

 proportion of the most powerful and fierce species, organized to 

 submit to some law of decreasing vitality, yet more than to a 

 cataclystic destruction. 



Hi re, then, we have the heads of those preliminary consider- 

 ations, which demand some notice of the great disturbances 

 that have affected the earth's surface, since the tertiary period 

 came into operation, and our present zoology started into being. 

 Next will be found requisite a few details on the bone deposits 

 before mentioned, by whatever agency they may have been 

 formed ; for, as by the former, the primordial nations may have 

 been forcibly scattered, so, by the latter, their actual existence 

 in regions now s>r:arated by whole oceans, appear to be indi- 

 cated. 



