INTHODITTION 



\Vcst\vard from tlio point wlicrc it strikes the 

 Yellow Kiver near lle-k'ou this boinulary is the 

 natural one, heinc: marked, first by a scetion of 

 tlie river, llien by the sandy edges of the Ordos 

 Desert, next by a seeond streteh of the Yellow 

 River, and finally by the southern border of the 

 Gobi Desert. 



Eastward from He-k'oii it is more difTicult to 

 traee 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 ^^'all 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 wTiter has been able 

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



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