180 RESEARCH IN CHINA. 
The Huang-t’u is believed to be older than the later faulting at least, and 
probably has been faulted. The fact that a fault-scarp extends out into 
the plain beyond the solid rock mass (Fig. 55) seems to be direct evidence 
to that effect, if it be substantiated. But those who doubt the recency 
of decided displacements may question whether the Huang-t’u could long 
maintain itself upon the slope. 
Northwesterly winds sweep loess in great quantities up onto the lower 
slopes of the range; this can not be questioned, but it seems hardly prob- 
able that it can accumulate there under present conditions of alternating 
wet and dry seasons. In a subsequent chapter I discuss the climatic 
fluctuations suggested by the occurrence of the Huang-t’u and have 

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Fic. 56 (Willis) —Near Hua-chéu, Shen-si. Profile of the northern slope of the Ta-hua-shan, showing 
its peculiar convexity and the interpretation of the surface as that of a normal fault. The curve 
is believed to indicate a revolution of the mountain mass about some fulcrum within it. ‘The rise 
of the Huang-t’u formation upon the lower slopes of the mountain is attributed either to faulting 
or eolian deposition. 
attributed obvious wind-drifts of loess to a drier episode than the present. 
Thus I entertain the hypothesis that both faulting and eolian deposition 
have been instrumental in placing the Huang-t’u on the slopes of the 
Ta-hua-shan, high above the plain. 
With the western termination of the Ta-hua-shan fault that range 
sinks away and the plain of the Wei widens some 15 miles, 25 kilometers, 
or more to the south, to the base of the Ts’in-ling-shan. This mountain 
range is again characterized by a remarkably straight front and by trian- 
gular facets cutting the spurs; it does not, however, exhibit the extremely 
abrupt rise from the plain which marks the Ta-hua-shan, at least not along 
