PHYSIOGRAPHY OF NORTHWESTERN CHINA. 233 
The condition which has given the Sha-ho the opportunity for vigorous 
growth is the elevation of the mountain mass of northern Shan-si above 
the district of Féu-p’ing-hién, in which the Sha-ho was already developed. 
We have, in the ragged spurs of the southeastern slope from the divide 
above Lung-ts’iian-kuan to Féu-p’ing-hién, the scarcely recognizable rem- 
nants of the older surface, that has been tilted and thoroughly cut to 
pieces by the accelerated and rapidly growing consequent streams. 
The T’ai-shan-ho, Hu-t’o-ho, and tributaries.—The ‘T’ai-shan-ho has 
a general southwesterly course. It rises in Pre-Cambrian rocks of the 
T’ai-shan complex and Wu-t’ai schists, and flows from them into a syn- 
clinorium in the Paleozoics. Disregarding the minor details of its windings, 
it is adjusted to the structure of the formations and occupies a synclinal 
valley, down which it flows in the direction of the pitch. It seems prob- 
able that it is a very ancient stream, which originated in a syncline on 
the Shan-si coal-measures at the time of the Post-Paleozoic folding, and 
has survived the vicissitudes of erosion and uplift. Its position is now 
very vulnerable on account of its elevation above the low valleys of east- 
ward flowing streams like the Sha-ho. 
The T’ai-shan-ho is indifferent to the relations of hard and soft rocks. 
The schists upon which it takes its rise yield far more readily than the 
limestones in which it has its lower course, but it leaves the wider valley 
for the narrower canyon without any evidence of adjustment to the resist- 
ance of the rocks. Its principal tributaries do likewise; heading in the 
southwestern prong of the Wu-t’ai range, they flow across the lowlands 
of the loess basins, which are cut out of soft Pre-Cambrian slates, and 
enter deep canyons in the Paleozoic limestone in order to join the ‘T’ai- 
shan-ho. This is true not only of the smaller streams, but even of the 
Hu-t’o-ho, the largest of the region, which, having its sources far to the 
north, flows southwesterly into the great Hin-chéu basin, winds to the 
northeast through a narrow pass into the Tung-yii basin, and then plunges 
into the canyon to join the T’ai-shan-ho in a general southeasterly course. 
We may describe the valley of the Hu-t’o-ho above Hin-k’ou as one 
which is adjusted both to the structure and to the softer rocks. It lies 
approximately parallel to the strike of the schistosity and folding in the 
Wu-t’ai range, and is bounded on the west by escarpments of the Sinian 
limestones; that is, it has developed in a zone of weak schists below the 
base of the Paleozoic. It, also, is probably an ancient river. Beyond 
the Hin-ché6u basin the natural course of the Hu-t’o-ho is through the 
Shi-ling to the basin of T’ai-yiian-fu, where it would join the Fén-ho and 
pursue its way down the graben of central Shan-si. We are not able to 
prove, by the occurrence of river gravels or other direct evidence, that 
