SINO-MONGOLIAN FRONTIER 
on the western margin of the same plain can only 
be explained by the existence of a fault, such as I 
have just described. Indeed there is no reason 
why a fault should not occur here, for further 
south and in an almost direct line with it a similar 
fault occurs, running in a direction slightly west 
of south, along the eastern side of the O Shan. 
In this also the downthrow is on the east. Richt- 
hofen, also, came ‘to the conclusion that there was a 
fault along the north-western margin of this plain. 
We put up at Huang-t’u-tsai, the place which 
gives its name to the Huang-t’u formation, a name 
given by Bailey Willis to the loess and various 
other Quaternary deposits of North China. 
The following day we continued down a dry 
stream bed and finally came out upon the T’ai-yiian 
Fu plain once more. 
PART 3 
THE GEOLOGY OF THE UprerR FEN Ho Basin, 
WESTERN SHANSI 
The geology of the country lying north-west 
of the T’ai-yiian Fu plain, owing to the extensive 
fault running down its north-western margin, is 
in many ways a repetition of that of the country 
traversed by the Chén-T’ai Railway. A new 
feature, however, is presented in the form of 
extensive outcrops of plutonic and metamorphic 
rocks. 
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