PHYSIOGRAPHY OF NORTHWESTERN CHINA. 227 
areas covered by the Huang-t’u are, in certain stretches, sunk in deep 
canyons, which are confined by steep slopes in the Pre-Cambrian rocks 
and in the Paleozoic limestones are walled by bold cliffs. These character- 
istics are features of youth, and the canyons compare in appearance and 
depth with the great normal fault-scarps of the Ki-chéu-shan and the 
Ho-shan. 
The four groups of features thus recognized occur widely distributed 
throughout northwestern Chi-li and northern and central Shan-si. In our 
journey we traversed them for a distance of more than 500 miles, 800 
kilometers. They are, therefore, not accidents of a local character, but 
wide-spread physiographic types, which are as significant records of the 
later history of southeastern Asia as the geologic formations are of the 
Paleozoic and Pre-Cambrian history. The physiographic stages may be 
defined, named, and ordered in sequence, much as we would arrange and 
interpret the members of a stratigraphic succession. In so doing we shall 
find that the four types are more or less widely distributed and lie in 
various relations to one another, both in horizontal extent and in altitude. 
We shall be obliged to recognize that these relations can not have devel- 
oped as they now exist without interaction of the processes of mountain 
growth and mountain sculpture, and that not only changes of elevation, 
but also changes of climate, have been involved in the development of 
the history. 
In what follows, the four stages of physiographic development are 
designated: Pei-t’ai, the oldest, T’ang-hién, Hin-chéu, and Fén-ho. They 
are believed to cover much of the Tertiary and the Quaternary. 
PEI-T’AI STAGE. 
In the preceding pages reference has repeatedly been made to the 
rounded forms of the high summits of the Wu-t’ai-shan, of which Pei-t’ai 
is not only one of the highest but also the broadest. Its aspects are repre- 
sented in the view (Plates XXXII and XXXIIJ) and in the panorama 
of the Wu-t’ai-shan on atlas sheet E I. We take this broad flat form 
to represent a stage of erosion of advanced old age, the nearest approxi- 
mation to a peneplain which we found in the course of our journey. The 
surface lies above all other features, and consequently is older than they. 
This oldest and most aged form, which is represented in the rounded sum- 
mits of the Wu-t’ai-shan, we name, from the conspicuous and characteristic 
dome in which it is best exemplified, the Pei-t’ai surface. Considered as 
a phase of topographic development, which was reached through prolonged 
erosion, we may designate it the Pei-t’ai stage; and the corresponding epoch 
may be called the Pei-t’ai epoch. 
