great bluff cutting across the valley — rises to a height of about 200 feet above 

 the stream-bed (Plate 46). 



At Ho-shui Hsien the bed-rock is chiefly in the form of dark-maroon or 

 grey shale, finely laminated. This gives place at Ch'ing-yang Fu to grey 

 sandstone with marked bedding. Immediately west of this city the loess 

 plateaux commence again. The country is noticeably drier than that to the 

 east, and the plateaux continue for about sixty miles, ending abruptly at 

 Ch^n-yiian Hsien. 



From here westward, the loess formations become much deeper and less 

 regular. The bed-rock rises gradually and is no longer perfectly horizontal. 

 Immediately west of Ch^n-yiian Hsien, the sections exposed on the side of the 

 valley show a red sandstone with marked bedding. It dips towards the west 

 at an angle of 20°. This is very clearly shown in the accompanying 

 photograph (Plate 57) of a view looking westward about five miles west of 

 Ch^n-yiian Hsien. 



The sedimentary formations from Ch6n-yuan westward rise steadily in 

 altitude till the Liu-p'an Shan are reached. This great range of mountains 

 (8000 to 10,000 feet high), composed of crystalline rocks, and extending from 

 north-west to south-east, lies to the west of Ku-yiian Chou and Wa-t'ing and 

 may be considered as the western rim of the great North Shensi basin. The 

 highest peaks are very precipitous, and resemble the Chiao-ch'eng Shan of 

 Western Shansi in their formation. The lower peaks are composed of lime- 

 stone, through which run many deep ravines. 



Ku-yiian Chou is situated in an immense loess basin, bounded north, east 

 and south by hills of sedimentary origin, and on the west and south-west by 

 the Liu-p'an Shan. On the western side of this range the formation is chiefly 

 of limestone, at a higher level than the sedimentary rocks to the east of the 

 range. 



From Ku-yiian the path lies in a general south-westerly direction till 

 Ching-ning Chou is reached. Immediately north of this city the limestone 

 formations are deeply cut through by a streani coming down from Liu-p'an 

 Shan. Westward from Ching-ning Chou the loess deposits increase 

 enormously in depth. High loess-covered mountains occur, divided by deep 

 ravines, and the substratum appears in only a few places. A photograph of 

 one of the deep canons is given (Plate 39). This was taken at Ying-t'ao-ho 

 immediately east of a high loess pass, and about sixty miles west of Ching- 

 ning. It is typical of the formations that occur throughout this area as far as 

 Hsiao-shui-tzu, near Lan-chou Fu. In places the loess is replaced by a dark, 



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