194 RESEARCH IN CHINA. 
of wind drift and scour, which would naturally be imposed upon a body of 
material so soft as the Huang-t’u. 
In the basin of Huang-t’u-chai (atlas sheets B II and B III) the 
Huang-t’u formation is typically developed in various phases. South 
of the Shi-ling is a wide plain at an altitude of 3,300 to 3,500 feet; above 
3,500 feet the hitherto gentle slope grows steeper and, between 3,600 and 
4,000 feet, becomes tangent to the rock slopes of the hills. From north to 
south the plain is continuous from the Shi-ling (altitude 3,550 feet, 1,082 
meters) to the margin of the bluffs above the channel of the northeastern 
branch of the Fén-ho, and it extends beyond to the southeastern hills. 
Toward the southwest it descends to the junction of the valley with the 
north branch of the Fén-ho, which opens upon the basin of T’ai-ytian-fu. 
This plain is a surface of the Huang-t’u, which, in its northern portion, 
exhibits typical relations with the environing hills. 
The body of Huang-t’u beneath the plain is being dissected by autog- 
enous canyons, some of which are 230 feet, 70 meters, deep and are the 
deepest we saw in the formation. They are locally cut down to bed-rock. 
The headward growth of these canyons is very vigorous, as is shown by 
changes which they have made necessary in the location of the highway, 
but only the main stream reaches across the basin. It is fed from a some- 
what extensive watershed in the eastern hills, and may not have had an 
autogenous growth in the plain. Its northern laterals end abruptly in 
canyons in the Huang-t’u, exhibiting a transient phase which exists only 
while the ravine is developing across the plain; and it is evident from the 
moderate length of the canyons that conditions have not long been favor- 
able to their development. In recent time one or both of two conditions 
have changed; either the plain has been raised relatively to the level of 
discharge of the main stream, or a desert climate has been replaced by a 
_less arid one, or both changes have occurred. 
The constitution of the Huang-tu in the plain is similar to that else- 
where throughout the northern Loess Basins. In the central part of the 
basin the material is largely loess and very fine sand, with some reddish 
clay and coarser sand. About the margins, drifted slopes consist wholly 
of loess, but, where streams debouch, the red soil and coarser wash they 
bring is widely spread and is interbedded at various levels in a manner to 
indicate that they were active from season to season, concurrently with the 
winds. At higher levels, as we observed on the summit which was occupied 
as a triangulation station west of the basin, there is a deep covering of 
reddish residual soil, which at the bottom contains bits of decayed lime- 
stone and is overlain by 10 to 20 feet, 3 to 6 meters, of loess, This soil 
