INTRODUCTION 



Westward from the point where it strikes the 

 Yellow River near He-k'ou this boundary is the 

 natural one, being marked, first by a section of 

 the river, then by the sandy edges of the Ordos 

 Desert, next by a second stretch of the Yellow 

 River, and finally by the southern border of the 

 Gobi Desert. 



Eastward from He-k'ou it is more difficult to 

 trace a natural boundary, as the whole country is 

 broken up by irregular ranges of hills and moun- 

 tains interspersed with wide river valleys, which 

 in some instances assume the dimensions of plains. 



On the whole the course of the outer loop of the 

 Great Wall may be said to define most satisfac- 

 torily the natural boundary. Especially is this 

 the case immediately north and north-west of 

 Kalgan, where a line of high cliffs of volcanic 

 origin marks the edge of what is generally known 

 as the Mongolian Plateau. 



From Kalgan the Wall runs first east and then, 

 after making a big loop to enclose the valley of 

 Pei Ho, turns south-east, following the crests of 

 the mountain ranges, finally ending abruptly on 

 the sea coast at Shan-hai-kuan (lit. Mountain-sea 

 pass). 



The line of demarcation between the land 

 actually occupied by the Mongols on the one hand 

 and the Chinese on the other follows the political 

 boundary, but, so far as the writer has been able 

 to observe, the floral and faunistic, as well as the 



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