The geographical distribution of animals, with a study of the relations ...

114 DISTRIBUTION OF EXTINCT ANIMALS. [part ii.with almost all the forms now living, produced a rich and variedfauna such as we now see only in the open country of tropicalAfrica.During all this period we have no reason to believe thatthe climate or other physical conditions of Europe were morefavourable to the existence of these animals than now. We mustlook upon them, therefore, as true indigenes of thecountry, andtheir comparatively recent extinction or banishment as a remarkablephenomenon for which there must have been some adequatecause. What this cause was we can only conjecture ; but itseems most probable that it was due to the combined action ofthe Glacial period,and the subsidence of large areas of land ouceconnecting Europe with Africa. The existence, in the smallisland of Malta, of no less than three extinct species of elephant(two of very small stature), of a gigantic dormouse, an extincthippopotamus, and other mammalia, together with the occurrenceof remains of hippopotamus in the caves of Gibraltar, indicatevery clearly that during the Pliocene epoch, and perhaps duringa considerable part of the Post-Pliocene, a connection existedbetween South Europe and North Africa in at least these twolocalities. At the same time we have every reason to believethat Britain was united to the Continent, what is now the GermanOcean constituting a great river-valley. During the height ofthe Glacial epoch, these large animals would probably retire intothis Mediterranean land and into North Africa, making annualmigrations' northwards during the summer.But as the connectingland sank and became narrower and narrower, the migratingherds would diminish, and at last cease altogether ;and when theglacial cold had passed away would be altogether prevented fromreturning to their former haunts.Miocene Peeiod.We now come to a period which was wonderfully rich in allforms of life, and of which the geological record is exceptionallycomplete. Various lacustrine, estuarine, and other deposits inEurope, North India, and North America, have furnished such a