6 The Value of Paleontology. 
more prominent among which are the Australian, the South Amer- 
ican,and the temperate lands of the Northern Hemisphere. Each 
of these possesses many peculiar forms of life not now found else- 
where. Has this distinction always prevailed? Paleontology 
answers decidedly in the affirmative, so far as extinct mammalia 
are concerned, There seems to be no doubt that the faunal dis- 
tinctions 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 dis- 
covery of the great similarity between the extinct forms of the 
Northern Hemisphere and the living or more modern ones of the 
Southern Hemisphere faune. The Jurassic character of much of 
the Australian fauna is known, while prevalent types of South 
America and Africa can be shown to have much relation to Eo- 
cene types of the north. In North America and Europe, tapirs, 
opossums, coatis, civets, kinkajous, lemurs.and toxodonts belong 
to the Eocene; now these animals characterize the southern con- 
tinental life, or as is the case with toxodonts, have but recently 
_ become extinct there. This mode of defining those faunz is not, 
however, exact, since many modern types have found their way 
into them, especially in the case of Africa. 
How then is life significant of chronological station in the 
earth’s strata? Since very many forms of animals are so widely 
spread and at the same time so distinctly limited in range on the 
earth’s surface to-day, the same order must have prevailed in past 
time and have been of equal significance. That this law of uni- 
formity has prevailed in the past as in the present is amply proven 
by the paleontology of a single zodlogical area taken by itself. 
The apparition of types over the northern land area has been nearly 
universal. This fact has only been placed within our reach by 
modern investigations in North America; for until the sister 
continent of Europe-Asia was explored, no one could be sure 
what degree of individual peculiarity her extinct hfe might 
present. Now it is certain that the succession of Tertiary 
beds was mutually similar, and that the cotemporaneous deposits 
contained in a large degree similar life, and that interme- 
diate stages of the one can be properly intercalated in the 
vacant interspaces of the other. The resemblances between 
