of loess. Except at the edges, these successive layers are practically horizontal. 
I will refer to this as the North Shensi basin, and will deal with it more 
closely in my remarks on the Huang-t’u formation. 
About fifteen miles west of Lin Hsien a very peculiar formation 
occurs. Three peaks, composed chiefly of granite, pierce through the 
Huang-t'u mantle, and rise to an altitude of from 6000 to 7000 feet. The 
peaks, which go by the name of Ch’ing-ting Shan (‘clear summit moun- 
tains’) run roughly in a line, north and south, their bases covering a square 
of five miles to the side. All round are loess hills. So far as could be 
gathered, these isolated peaks are the result of folding; but on this point I 
would not care to offer a positive opinion. 
Westward, to the Yellow River, the country consists of loess lying upon 
a thick layer of sandstone. Through the latter, streams flowing towards the 
Yellow River in a general westerly direction have cut down to a depth 
commencing at from 20 to 30 feet and gradually increasing to about 300 feet 
in its bed. This sandstone doubtless belongs to the Shansi formation; it is 
perfectly horizontal in stratification, and nowhere were any faults noticed. It 
is in the form of freestone, and is admirably illustrated in the accompanying 
photograph (Plate 9g). 
On the western bank of the Yellow River, the same formation extends to 
the borders of the Ordos, though the depth of the sections exposed along the 
sides of the river-valleys becomes less and less till only along the largest rivers 
is there any outcrop. 
At Yii-lin Fu the loess formations give place to a peculiar, hard, purplish 
rock containing a certain percentage of sand. Though not nearly so hard, it 
closely resembles shale, and doubtless only requires pressure to be converted 
into it. This hardened, sandy mud, or mudstone, protrudes through the thick 
layer of loose sand in the form of low rounded hills; one of which appears 
in the photograph of the sand-dunes (Plate ro). 
The sand that exists in this district, is of the same yellowish fawn tint as 
the loess, and is from fifty to one hundred feet deep. It is very soft and 
loose, and in the river-beds and damp ravine-bottoms forms dangerous quick- 
sands. About Yii-lin Fu itself the sandstone, where visible, is of a pale 
greenish colour; but further to the south-west along the Ordos border it is of 
a brick-red. A deep bed of this red sandstone occurs at the head of the Yen 
Shui valley, a few miles south of Ching-pien. Here the cliffs rise to the 
height of some 200 feet, whilst the waters of the Yen Shui are stained a deep 
ted. Red sand is deposited along the valley near Yen-an Fu. 
122 
