260 RESEARCH IN CHINA. 
drift, but is probably also to some extent original, and which, under present 
conditions of slope and climate, is now being eroded, as is shown by the 
numerous deep gullies that reach into it. 
The basin of T’ai-yiian-fu and the mountain ranges which surround 
it present features identical in general aspects and relations to those of 
the more northern Loess Basins and their environing mountains. The 
basin, which is deeply filled with the Huang-t’u formation and which 
contains, no doubt, extensive deposits of that formation from the earliest 
to the latest, is regarded as a downwarp of the Fén-ho epoch. The moun- 
tains which lie along its northwest margin show a tilted surface of older 
topography, which is now being dissected, but which has not progressed 
far toward the ultimate obliteration awaiting it. On the southeast side 
of the basin a similar warped surface rises to the mountains, which are 
the northern extension of the Ho-shan. From that upwarp the fault- 
scarp of that great range extends south, having the same genetic relation 
to the warped surface which the fault-scarp of the Ki-chéu-shan possessed 
to the warped surface from which it springs. 
The valley of the Fén-ho, considered with reference to the upwarp 
of the Ho-shan and the O-shan, is a graben. Our reason for assigning 
the sinking of the graben to the Fén-ho epoch is that the fault-scarp of 
the Ho-shan so far as we could observe it, and that of the O-shan as 
described by von Richthofen, have only suffered a degree of erosion of 
the same order of development as that of the Ki-chéu-shan. 
Across the valley of the Fén-ho, extending in an east-west direction 
between Ling-shi-hién and P’ing-yang-fu, is the upwarp through which 
the Fén-ho, as an antecedent stream, has cut the canyon that the highway 
avoids by crossing the high passes of the Si-sin-ling and Si-yau-ling. 
Although we did not see the deeper parts of this canyon, its character 
south of Ling-shi-hién, where it is 400 feet, 120 meters, deep, in relation 
to the features of the T’ang-hién and Hin-chéu epochs which characterize 
the uplands, sufficiently mark it as belonging to the Fon-ho epoch. 
The basin of P’ing-yang-fu and the lower portion of the Fén-ho valley 
constitute a depressed area in the southern part of the graben of Shan-si. 
They present no distinctive features which would enable us to assign 
them to any time later than the Hin-chdéu epoch, but they are surrounded 
by upwarps of the Fén-ho time. 
The ridge which extends east and west, south of the junction of the 
Fén-ho and the Kii-ho, is one of the youngest features assignable to the 
Fén-ho time. It has an elevation of about 1,200 feet, 365 meters, is still 
covered by the Huang-t’u formation, and is characterized by the extreme 
youth of the autogenous gulches which are being cut in the mantle of 
