18 GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 



























How beautifully these material forces act, binding each 4 
species to a special home, from which it may not wander and q 
live. Nature places the bounds, the ocean waters may — 
sweep by, but they cannot bear along the life which throngs E 
them. These inorganic causes alone constitute the limits of — 
faune, and can it be doubted that faune really exist in na- — 
ture, when it is fully understood that all their modifications q 
and complications are results of revolutions in these causes 4 
themselves? Let us look at some of these revolutions,— — 
changes in topography, in temperature, and in ocean cur- a 
voniar-for thus far we have seen only how the diffusion of 
ocean species is limited by secondary causes. 4 
We should begin when the first species of the present 3 
faunæ began to appear, and trace the changes to the present ; 4 
but the data are very imperfect, and we can get only glimp- 
ses of these changes, yet enough to indicate some of t 
effects they have produced in the distribution of species. 
living in the Tertiary period, when Europe was scarcely 
more than an archipelago, when the lower Mississippi valley 
was a part of the Gulf of Mexico, and while Florida and 
the whole border of the southern Atlantic States were still 
swept by the waters of the ocean. But these few recent 
species were not then in their present homes; they have 
wandered, like the early races of men, southward. 
The European fossil land faune and flore indicate very 
clearly a change of climate from tropical to temperate during 
the Tertiary period, and in the marine climate there was 4 
similar change. On the western shores of France, along the 
vallies of the Loire and the Ardour, there are deposits of f 
early Tertiary mollusks and echinoderms, a large part 
them extinct or unknown species, but a small part at least 
are still living in the Atlantic Ocean. These species 
not, however, now found on the coast of France, but eig 
CE 
