258 RESEARCH IN CHINA. 
In usual relations features of the Fén-ho stage are cut within valleys 
of the T’ang-hién and Hin-chdéu stages. For example, in the Wu-t’ai-shan 
we may observe, in sequence from above downwards, the Pei-t’ai surface, 
the valleys of the T’ang-hién stage, and the canyons of the Fén-ho stage. 
Similarly, in the Ki-chéu-shan we see the mature topography of the T’ang- 
hién epoch, still in part covered with the loess of the Hin-chéu, but deeply 
cut by the canyons of the Fén-ho time. A similar relation holds on the 
Fon-ho between Ling-shi-hién and P’ing-yang-fu, where the river cuts 
its channel across the upwarped T’ang-hién surface that is covered with 
the Huang-t’u formation. A less familiar though not unusual relation 
exists between the warped slopes or fault-scarps of the Fén-ho stage and 
adjacent surfaces of older stages. The latter have been, so to speak, 
thrown by the warping or faulting; they have been elevated or depressed, 
tilted or dislocated. The tilt or dislocation is a characteristic acquired 
in Fén-ho time, which serves to differentiate the warp or scarp from the 
not-warped or not-faulted areas. The warps, which, as they become 
dissected, lose their earlier topographic aspects, thus take on a phase 
peculiar to the Fén-ho stage. This phase is cut upon the older features 
within the tilted areas, but if considered in relation to adjacent areas 
is seen to form a connecting slope between the elevated and depressed 
sections, which still exhibit features of earlier stages. This relation is 
seen in descending from the Wu-t’ai-shan to the Loess Basins. Leaving 
the Pei-t’ai surface and the ridges which represent the T’ang-hién stage, 
we pass down over a warped surface that is cut by ravines of Fén-ho time, 
to the aggraded valleys of the T’ang-hién and Hin-chdéu stages. 
Such warping and faulting of a topographic surface introduces into 
physiographic studies problems of identification not unlike those met in 
tracing folded or faulted strata. 
We may now enumerate some of the features assigned to the Fén-ho 
epoch. It should be borne in mind throughout that the topographic phase 
preceding the Fén-ho is believed to have been one of very mature relief, 
and that the valleys had been extensively aggraded with the Huang-t’u 
formation. 
Along the line of our route from Pau-t’ing-fu to Wu-t’ai-shan the 
valley of the Sha-ho in northwestern Chi-li above Féu-p’ing-hién, espe- 
cially above Li-ytian-p’u, first suggested the recency of mountain growth. 
Its obvious autogeny and the vigorous development of the gulches occupied 
by its headwater rivulets, as well as the aggressive attitude of the Sha-ho 
with reference to the T's’ing-shui-ho, are characteristic of a stream which 
is growing on a recently warped slope. The fact that so aggressive an 
agent had not yet succeeded in cutting back into the older valleys of the 
mountains indicated that it had not long been actively engaged in its 
