PHYSIOGRAPHY OF NORTHWESTERN CHINA. 223 
drained and, after the bottom had been partly eroded bya stream, covered 
by the general deposit of loess. 
At its junction with the Kii-ho, the valley of the Fén-ho is a wide 
flood-plain, the flat surface of a modern loess deposit. In this broad plain 
the Fén-ho changes its course and flows westward to the Huang-ho; but 
southward, in the direct line of the upper river, is a low pass by which it 
formerly continued to P’u-chéu-fu. The reason for the diversion is the 
growth of a very recent upwarp, across which the stream for a long time 
held its way, until it was captured by the tributary of the Huang-ho, whose 
course it now follows. 
The evidence of the upwarp is found in the character of the region 
which extends east and west, south of the diverted Fén-ho. It is a flat 
summit about 1,200 feet, 370 meters, above the river, completely covered 
with loess, on the northern slope of which there is a group of loess 
canyons of extremely recent development. They extend to the summit 
of the ridge, but have not yet crossed its even sky line. In the upper 
cliffs one may see, interbedded with the loess, a band of greenish gray 
marl, a stratified deposit which could not have been laid down in its pres- 
ent position. Around the western end of this ridge there extends a broad 
valley, which is probably 250 feet, 75 meters, above the present level of the 
Foén-ho, and is filled with alluvium. The alluvium consists of loess and 
stream gravels, and in every way corresponds with the Huang-t’u formation. 
It is characterized by especially abundant snail shells. The road crosses 
the pass without appreciable climb, and descends very gently southward. 
A wide plain opens toward the south, and across the plain runs an old river 
bed, following the bases of alluvial cones and dividing downstream after the 
manner of distributaries of a delta. The channel is occupied by a rivulet, 
and is now floored by sandy clay about 100 meters in width. From this 
clay salt is obtained by digging shallow holes, in which brine rises. 
The broad flat top of the ridge, the vigorous but very youthful canyons 
in the loess on its slope, and the abandoned river channel in direct line with 
the Fén-ho, appear to leave no question that we have here an instance 
of warping, which has produced an elevation of 1,200 feet, 370 meters, 
which was so rapid as to divert the river, and is so young that the steep 
slopes have not yet been denuded of the soft Huang-t’u. 
In the discussion of the structural geology of southern Shen-si, the 
valley at the northwest base of the Féng-huang-shan was described and 
the face of the range was discussed as a mature fault-scarp. In this 
description of the physiographic features it will suffice to repeat that the 
face of the range is steep and characterized by those triangular facets, as 
terminations of the lower ridges, which are taken as direct representatives 
of the normal fault-plane. It was also stated that, as we went southwest- 
