PHYSIOGRAPHY OF NORTHWESTERN CHINA. Pa be" 
wind-gap at its head, I. It seems to be clear that there was a river, CGI, 
which formerly flowed parallel to the Sing-ho, but has been inverted by 
an upwarp along MN, resulting in the canyon of the antecedent Sing-ho 
and the diversion and inversion of its weaker neighbor. 
Another anomaly of the Wu-t’ai basin is the fact that it is invaded 
from the southwest by a branch of the Hu-t’o-ho, KL, which cuts in two 
the ridge between it and the Tung-yii basin. This is a case of growth of 
a brook through a divide along the strike of a zone of soft slate; but it 
calls attention to the fact that a surface like that east of the divide, having 
a gentle slope and being composed of the porous Huang-t’u, is a very 
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AARON Re 
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Fic. 57.—Map showing arrangement of tributaries tothe Hu-t’o-ho and Sing-ho, near Wu-t’ai-hién, 
Shan-si; reduced from the surveys by Sargent, atlas sheet CI. 
absorbent one. No stream forms on it, and unless it be gullied from a 
lower level it may, in appropriate situations, be an area of accumulation 
by wind drift. Had the Huang-t’u surface not been an absorbent one, the 
Sing-ho might have contested the divide it has now lost to the Hu-t’o-ho. 
The Tung-yti loess basin is a simple river valley directly parallel to 
that of the Sing-ho and Shi-t’ou-ho, from the Wu-t’ai-shan to the T’ai- 
shan-ho. ‘The original small stream is now joined by the Hu-t’o-ho, the 
master river of the region, which comes through a rock gap west of Tung-yii. 
The fact that the Hu-t’o-ho at this point crosses a ridge, in a relatively 
narrow gorge of youthful aspect, in a course directly opposed to the south- 
