OBSERVATIONS IN CENTRAL SHAN-SI. 181 
considerable stretches of its extent. As seen from Si-an-fu it appears to 
approach in height and boldness the Ta-hua-shan, but being 15 miles, 52 
kilometers, or more distant its character evaded analysis. At Chdéu-chi- 
hién, where we saw it closely, it presents the typical aspects of a normal 
fault-scarp, which involves not only the mountain block of Pre-Cambrian 
rocks, but also the loess of the valley plain. The features are expressed 
in the topographic and geologic maps (atlas sheet a 1) andin Plate XXII, 
giving views taken from near the base, at Hei-shui-k’6u, looking east 
and west along the front. ‘This portion of the range is much less abrupt 
in its rise from the plain than it is further east, and toward the west it 
flattens out into a long gentle upwarp (see Plate XXII, Fig. B). 
GENERAL RELATIONS OF THE NORMAL FAULT SYSTEM. 
The remarkable arc of normal faults thus followed throughout 450 
miles, 725 kilometers, from northeast to southwest, extends around the 
southeastern boundary of the high plateaus of Mongolia, but lies well 
within the mountain ranges west of the great plains of China. It defines 
the great intermontane valleys of the Fén-ho in Shan-si and of the Wei-ho 
in Shen-si, and the courses of these streams, as well as that of the lower 
Huang-ho, are determined by the displacements. The F6én-ho lies in 
the graben of central Shan-si; the Wei-ho flows along the southern margin 
of the downthrown slope of northern Shen-si; and the Huang-ho, after 
flowing southward on that slope for several hundred miles, turns sharply 
at the base of the Ta-hua-shan, and passes out between the ranges on the 
lower edge of the tilted block. The normal fault system is thus seen to 
be a feature of notable magnitude in the structure of the continent. 
One who regards the features of eastern Asia as a succession of steps, 
descending from the high plateaus southeastward to the plains, would 
expect the downthrow of these faults to be on the eastern or southern 
sides of the fault-scarps, which would face accordingly toward the east 
or south. With the exception of the relatively small fault of the O-shan, 
which marks the western side of the graben of central Shan-si, this is 
not the case. The downthrow is uniformly on the northwest, west, or 
north, and the great scarps face accordingly to the west or north. They 
overlook the country in that direction, and it thus appears that the descent 
from the high plateau to the plain is here interrupted by a feature of the 
first magnitude. ‘Toward the east and south from the system of normal 
faulting, we have extensive mountain masses, which attain altitudes of 
5,000 to 12,000 feet, 1,500 to 3,600 meters, and from which the descent to 
the plain is in part by faulting, with the downthrow on the eastern side, as 
described by von Richthofen for southern Shan-si, and in part by gently 
inclined warped surfaces. 
