SINO-MONGOLIAN FRONTIER 



as marbles. All the granite up this way is of a 

 pale buff colour. 



The hills south of the lake are of basalt, as also 

 are those on the west as far as the pass beyond 

 Ning-yiian. Here an extensive outcrop of granite, 

 a continuation of that occurring north of the lake, 

 extends as far as Yang-p'o-yao-tzu. From this 

 point to the edge of the K'uei-hua-ch'eng plain 

 basalt occurs, showing fine columnar structure. 

 The basalt and granite are frequently superim- 

 posed by loess, but not to any very great depth or 

 extent. 



No outcrops of any kind occur on the plain, 

 which is mainly alluvial, with patches of wind- 

 deposited sand. 



The T'ai Hai (lake) lies in an immense basin some 

 twenty miles long and ten miles wide. This basin 

 is bounded on three sides by low hills of volcanic 

 formation, and on the fourth (the north) by high 

 mountains of granite. It is diflficult to explain 

 the existence of this hollow in which the lake lies. 

 The latter is said to be very deep in the centre. 

 At first one might suppose that it occupies the 

 crater of an extinct volcano, but this is by no 

 means certain. Further investigation is needed 

 before such a theory can be confidently advanced. 

 It would, however, be interesting to know the 

 origin of all the basalt, so prevalent in this 

 country. 



Referring to the mountains north-west of K'uei- 



275 



