11 



XL 



Paleontology in its relation to geology is as yet partially empirical. 

 Thus, while its indications are definite for one locality, they have not identical 

 significance for all localities on the earth's surface. The lower we descend in 

 the scale of being, the more uniform over great areas are its phenomena ; but, 

 among higher animals, esjiecially vertebrates, the greater the geographical 

 peculiarities as compared with the stratigraphical. Professor Agassiz once 

 said that the e.xisting geographical fauusB are more distinct than the extinct 

 faunae of two consecutive epochs of geologic time; a statement justified by 

 many facts. Hence, it has been believed by some, that fossil vertebrates 

 cannot furnish conclusive evidence of the age of the rock-strata in which they 

 occur; for, say they, we have to-day existing on the Australian continent, 

 animals that approach more nearly to those found fossil in the Jurassic forma- 

 tions of Europe than to any now living on the latter continent ; so that, were 

 Australia to be presently submerged and her strata and fossils again brought 

 to light, the paleontologist would assert that the sun had not shone on that 

 land since the days of the Jura. And so he would were he not at the same 

 time a zoologist; just as the bare zoologist would err in the opposite direction 

 of assuming the modern age of the European Jurassic beds, because they 

 contain the living types of Australia. Thus, a foundation-fact of zoology 

 properly applied is essential to the paleontologist, namely, that the earth 

 now presents four or more distinct faunal areas, the more prominent among 

 which are the Australian, the South American, and the temperate lands of the 

 northern hemisphere. Each of these possesses many pecuHar forms of life 

 not now found elsewhere. Has this distinction always prevailed? Paleon- 

 tology answers decidedly in the affirmative, so far as extinct mammalia are 

 concerned. There seems to be no doubt that the faunal distinctions have a 

 very ancient origin, and are therefore to be first considered when estimating 

 the age of strata from the contained mammalian remains. The explanation 

 of this diversity is not yet attainable ; but an important advance has been made 

 by the discovery of the great similarity between the extinct forms of the 

 northern hemisphere and the living or more modern ones of the southern 

 hemisphere faunae. The Jurassic character of much of the Australian fauna 

 is known, while prevalent t3'pes of South America and Africa can be shown 

 to have much relation to Eocene types of the north. In North America and 

 Europe, tapirs, opossums, coatis, civets, kinkajous, lemurs, and allies of the 



