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

72 DISTRIBUTION OF ANIMALS. [part I.so clearly indicated as in some of the other regions, and they areadopted more for convenience than because they are very naturalor strongly marked.The first, or European sub-region, comprises Central andNorthern Europe as far South as the Pyrenees, the Maritimeand Dinaric Alps, the Balkan mountains, the Black Sea, and theCaucasus. On the east the Caspian sea and the Ural mountainsseem the most obvious limit ; but it is doubtful if they form theactual boundary, which is perhaps better marked by the valleyof the Irtish, where a pre-glacial sea almost certainly connectedthe Aral and Caspian seas with the Arctic ocean, and formedan effective barrier which must still, to some extent, influencethe distribution of animals.The next, or Mediterranean sub-region, comprises SouthEurope, North Africa with the extra-tropical portion of theSahara, and Egypt to about the first or second cataracts ; andeastward through Asia Minor, Persia, and Cabul, to the desertsof the Indus.The third, or Siberian sub-region, consists of all north andcentral Asia north of Herat, as far as the eastern limits of thegreat desert plateau of Mongolia, and southward to about theupper limit of trees on the Himalayas.The fourth, or Manchurian sub-region, consists of Japan andNorth China with the lower valley of the Amoor ;and it shouldprobably be extended westward in a narrow strip along theHimalayas, embracing about 1,000 or 2,000 feet of verticaldistance below the upper limit of trees, till it meets an easternextension of the Mediterranean sub-region a little beyond Simla.These extensions are necessary to avoid passing from the Orientalregion, which isessentially tropical, directly to the Siberian subregion,which has an extreme northern character ; whereas theMediterranean and Manchurian sub-regions are more temperatein climate. It will be found that between the upper limit ofmost of the typical Oriental groups and the Thibetan or Siberianfauna, there is a zone in which many forms occur common totemperate China. This is especially the case among the pheasantsand finches.