178 RESEARCH IN CHINA. 
downthrown slope of the Féng-huang-shan block, a few kilometers north 
of the fault which skirts the base of the Ta-hua-shan (Fig. 54). 
From Tung-kuan, where one crosses the river, loess-covered terraces 
extend in a long slope from the river southward to the base of the Ta-hua- 
shan. Further west, between Hua-yin-hién and Hua-chéu, on the southern 
side of the Wei valley, the Ta-hua-shan presents an extraordinarily pre- 
cipitous character (Fig. A, Plate X XI). The level plain of the valley extends 
directly to its base, and cliffs of granite rise probably 4,000 feet, 1,200 meters, 
to extremely rugged summits. The crest is deeply gashed. The forms 
produced by erosion are controlled by systems of vertical joints which 
extend in two directions, the one parallel to and the other transverse to 
a 
St 
L me T a at € V ij 
j Zp NN ANN IN ‘ 
“777 op 
Fic. 54 (Willis) —Tung-kuan-t’ing, Shen-si. Cross-section of;the valley of the Huang-ho, showing the 
general relations of the Féng-huang-shan on the north and the Ta-hua-shan on the south, and the 
position of the aggraded river valley along the southern, downthrown margin of the Féng-huang-shan 
fault-block. a= slope of the Féng-huang-shan; bc= irregular hills covered with loess; cd = terrace 
of the Huang-t’u formation about 38 meters above the river; d= channel of the Huang-ho; e= 
somewhat irregular surface of the Huang-t’u; f= upthrown block of the Ta-hua-shan. Horizontal 
and vertical scales indeterminate. 
the course of the range, and they give rise to cliffs estimated in one instance 
to be at least 2,500 feet, 750 meters, at an angle of 70° or steeper. Further 
westward, the attitude of these joints changes from verticality to a nearly 
horizontal position, and the aspect of the mountain forms becomes milder 
accordingly (see Fig. B, Plate XXI). But while the jointing thus controls 
erosion forms, the face of the range continues abrupt and straight as far 
as Hua-choéu, and clearly represents a recent fault-scarp. West of Hua- 
chéu the range declines, and finally turns southward. The continuous 
plane of the front, which is most conspicuous in the lower and steeper 
slopes, extends around the curve toward the south, and is more cr less 
covered with loess up to 800 or 1,000 feet, 250 or 300 meters, above the 
plain. Three miles, 5 kilometers, southwest of Hua-chéu, there springs 
from this slope a ridge or terrace, which presents a scarp about 700 feet, 
200 meters, high as seen from the valley plain, and extends westward. 
It has a very flat gently-sloping crest, and where cut through by a ravine, 
some 3 miles, 5 kilometers, further east, it is seen to consist of Huang-t’u 
tothe base. Its altitude at that point is between 300 and 4oo feet, 100 and 
