114 DISTRIBUTION OF EXTINCT ANIMALS. [PART II, 
with almost all the forms now living, produced a rich and varied 
fauna such as we now see only in the open country of tropical 
Africa. During all this period we have no reason to believe that 
the climate or other physical conditions of Europe were more 
favourable to the existence of these animals than now. We must 
look upon them, therefore, as true indigenes of the country, and 
their comparatively recent extinction or banishment as a remark- 
able. phenomenon for which there must have been some adequate 
cause. What this cause was we can only conjecture; but it 
seems most probable that it was due to the combined action of 
the Glacial period, and the subsidence of large areas of land once 
connecting Europe with Africa. The existence, in the small 
island of Malta, of no less than three extinct species of elephant 
(two of very small stature), of a gigantic dormouse, an extinct 
hippopotamus, and other mammalia, together with the occurrence 
of remains of hippopotamus in the caves of Gibraltar, indicate 
very clearly that during the Pliocene epoch, and perhaps during 
a considerable part of the Post-Pliocene, a connection existed 
between South Europe and North Africa in at least these two 
localities. At the same time we have every reason to believe 
that Britain was united to the Continent, what is now the German 
Ocean constituting a great river-valley. During the height of 
the Glacial epoch, these large animals would probably retire into 
this Mediterranean land and into North Africa, making annual 
migrations northwards during the summer. But as the connect- 
ing land sank and became narrower and narrower, the migrating 
herds would diminish, and at last cease altogether; and when the 
glacial cold had passed away would be altogether prevented from 
returning to their former haunts. 
MIocENE PERIOD. 
We now come to a period which was wonderfully rich in all 
forms of life, and of which the geological record is exceptionally 
complete. Various lacustrine, estuarine, and other deposits in 
Europe, North India, and North America, have furnished such a 
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