240 RESEARCH IN CHINA. 
tains on the east, which are the southern extension of the Ki-chéu-shan, 
and the plateau on the west, which is of the Ordovician limestones, appear 
also to be crowned by surfaces of typical mature character, but at a much 
higher level. It would follow that, in recognizing the identity of features 
of the T’ang-hién stage in the basin of Huang-t’u-chai and in the adjacent 
mountains, we must accept the evidence of their former continuity and 
admit that they have since been warped to different levels. 
In the valley of the Fén-ho, from the southern margin of the basin 
of T’ai-yiian-fu to a point south of P’ing-yang-fu, features of the T’ang- 
hién stage were recognized in mature topographic forms sculptured upon 
the sandstones and shales of the Shan-si series and covered by Huang-t’u; 
but the soft rocks are deeply cut by narrow ravines, and the older fea- 
tures are not readily recognized in detail. 
It is probable that the south slope of the Féng-huang-shan is also 
characterized by features of the T’ang-hién stage. It has a flat, slightly 
hilly surface, which is now tilted, but was formerly much more nearly 
level. In consequence of the tilting it is being dissected, yet the process 
has not proceeded far and the aspects of its features justify us in calling 
them T’ang-hién. 
In the several districts in which we find features that we assign to 
the T’ang-hién stage, there is but one characteristic upon which to base 
a correlation. It is that of physiographic maturity. Wide valleys, low 
relief, and the isolation of monadnocks as individuals or in groups, are 
the topographic characteristics common to all the areas placed in this 
class. In other respects there are marked differences between the dis- 
tricts. Thus with reference to altitude above sea: southeast of T’ang-hién 
the surface probably extends below sea-level, and in the vicinity of that 
city has an elevation of only 300 to 4oo feet, 90 to 120 meters. In the 
Wu-t’ai-shan the altitude of the ridges which are taken as representing 
the stage is from 5,000 to 5,500 feet, 1,500 to 1,650 meters. In the Loess 
Basins about Wu-t’ai-hién the elevation is 4,000 to 4,500, 1,200 to 1,350 
meters, and in the limestone mountains southeast of Wu-t’ai-hién and in 
the Ki-chéu-shan it is again higher, namely, from 5,000 to 6,000 feet, 
1,500 to 1,800 meters. In the valley of the Fén-ho the T’ang-hién surface, 
as there recognized, rises from 2,700 feet, 825 meters, in the vicinity of 
T’ai-yiian-fu to nearly 4,000 feet, 1,200 meters, between Ling-shi-hién 
and Ho-chéu, but descends again to about 2,600 feet, 800 meters, near 
P’ing-yang-fu. Thus it is apparent that altitude above sea is not a crite- 
rion by which we may distinguish features of the T’ang-hién stage. The 
total range in elevation within the area of our observation being from 
below sea to 6,000 feet, 1,800 meters, above sea, greater range is quite 
possible. 
