XXVvill INTRODUCTION. 
received its pliocene Mammalia; and the Zoologist finds 
this answer to accord with the known powers and habits 
of those Mammalia. It is true that the Elephant crosses 
rivers too deep for it to ford; but it swims heavily and 
slowly, the head and body quite immersed, and only the 
end of the trunk raised out of the water. The Hippo- 
potamus has been observed to go a short way out to sea 
from the mouth of its native African river. ‘“ The Tiger 
is seen swimming about among the islands and creeks in 
the delta of the Ganges; and the Jaguar traverses with 
ease the largest streams in South America. The Bear, 
also, and the Bison cross the current of the Mississippi.”* 
But these facts seem to me to form inadequate grounds 
for belief that those animals could cross a tidal current 
of sea, twenty miles in breadth. Still less can we suppose 
that the ponderous Rhinoceroses, the Hyenas, Wolves, 
Foxes, Badgers, Oxen, Horses, Hogs, and Goats; the 
smaller Deer, Hares, Rabbits, Pikas, or even the aquatic 
Rodents, could have reached this island from the Con- 
tinent, if the present oceanic barrier had interposed. The 
idea of a separate creation of the same series of Mammalia 
which existed on the Continent, in and for a small con- 
tiguous island, will hardly be accepted. M. Desmarest 
deduced an argument in proof that France and England 
were once united, from the correspondence of their Wolves, 
Bears, and other species known to have existed in this 
island within the period of history: the conclusion becomes 
irresistible when the same correspondence is found to ex- 
tend through the entire series of Proboscidian, Pachy- 
dermal, Equine, Bovine, Cervine, Carnivorous, and Rodent 
Mammalia, which characterized the two countries during 
the pliocene period of Geology. Thus the science of 
* Lyell, Principles of Geology, vol. iii. p. 33. 
