Geology and Natural History. 805 
of the animals :--the northern, into which the southern forms 
never penetrated, the latitude of Yorkshire being the boundary of 
the advance of the southern animals; the southern, into which the 
There were three climatal zones, marked by the varying range 
and Pyrenees being the limit of the range of the northern animals; 
and an intermediate area, in which the two are found mingled 
together. 
can therefore no longer be looked on as a hard and fast barrier 
Separating one fauna from another. If man be treated as a Pleis- 
t . 
could not pass westward until the barrier was removed by the ele- 
vation of the sea bottom between the Caspian and the Urals. : 
The same argument holds good as to the African mammalia, 
which could not have passed into Sicily, Spain, or Britain without 
a northward extension of the African mainland. : 
_The relation of the Pleistocene to the Pliocene fauna is a ques- 
tion of great difficulty. If the Pliocene fauna be compared with 
that of the Forest-bed, it will be seen that the difference between 
them is very great. The Pliocene mastodon and tapir, and most 
cally Pliocene is that furnished by the lacustrine strata of Auvergne, 
marine sands of Montpellier, and the older fluviatile strata 
Val d’Arno 
