72 DISTRIBUTION OF ANIMALS. [PART I. 
so clearly indicated as in some of the other regions, and they are 
adopted more for convenience than because they are very natural 
or strongly marked. 
The first, or European sub-region, comprises Central and 
Northern Europe as far South as the Pyrenees, the Maritime 
and Dinaric Alps, the Balkan mountains, the Black Sea, and the 
Caucasus. On the east the Caspian sea and the Ural mountains 
seem the most obvious limit; but it is doubtful if they form the 
actual boundary, which is perhaps better marked by the valley 
of the Irtish, where a pre-glacial sea almost certainly connected 
the Aral and Caspian seas with the Arctic ocean, and formed 
an effective barrier which must still, to some extent, influence 
the distribution of animals. 
The next, or Mediterranean sub-region, comprises South 
Europe, North Africa with the extra-tropical portion of the 
Sahara, and Egypt to about the first or second cataracts; and 
eastward through Asia Minor, Persia, and Cabul, to the deserts 
of the Indus. 
The third, or Siberian sub-region, consists of all north and 
central Asia north of Herat, as far as the eastern limits of the 
great desert plateau of Mongolia, and southward to about the 
upper limit of trees on the Himalayas. 
The fourth, or Manchurian sub-region, consists of Japan and 
North China with the lower valley of the Amoor; and it should 
probably be extended westward in a narrow strip along the 
Himalayas, embracing about 1,000 or 2,000 feet of vertical 
distance below the upper limit of trees, till it meets an eastern 
extension of the Mediterranean sub-region a little beyond Simla. 
These extensions are necessary to avoid passing from the Oriental 
region, which is essentially tropical, directly to the Siberian sub- 
region, which has an extreme northern character; whereas the 
Mediterranean and Manchurian sub-regions are more temperate 
in climate. It will be found that between the upper limit of 
most of the typical Oriental groups and the Thibetan or Siberian 
fauna, there is a zone in which many forms occur common to 
temperate China. This is especially the case among the phea- 
sants and finches. 
