218 RESEARCH IN CHINA. 
Huang-t’u formation, which here, as elsewhere, extends to the adjacent 
hills by its peculiar tangent curve; the same covering appears extensively 
on the summits of the hills, though eroded from their steeper slopes. 
From all higher levels the Huang-t’u is being eroded and redistributed 
by the torrential rains, the gravels being spread as alluvial cones upon 
the surface of the older Huang-t’u deposit, and the loess being carried out 
further into the plain and incorporated with it. The winds which sweep 
the bare surface during the seasons of drought and cold carry back some 
part of the loess and in a measure maintain the fringe that rises onto the 
slopes, but on the whole the process is one of denudation, and the mature 
forms of the topographic surface beneath the Huang-t’u are reappearing. 
The basin of Huang-t’u-chai lies immediately south of the Hin-chéu 
basin, and is connected with it by the continuous surface of the Huang-t’u 
formation across the Shi-ling Pass. Southward it opens as a valley of 
a branch of the Fén-ho into the basin of T’ai-yiian-fu, and forms a con- 
necting link between the latter and the Hin-chéu basin. Its character 
is rather that of a wide river valley than of a simple downwarp, it being 
relatively narrow and branching. We shall see that probably both erosion 
and warping have been effective in producing its present aspects. 
The principal branch of the Fén-ho, which flows through the basin 
of Huang-t’u-chai, has cut a wide channel some 300 feet, 100 meters, 
below the level plain of the basin, and canyons of unusual narrowness 
are rapidly growing back into the Huang-t’u formation. The highway 
follows down the sides of one of these, giving rather startling opportunities 
to look into its depth. In the bottom of another the underlying Sinian 
limestone is found, and the thickness of the Huang-t’u may be determined 
to be about 230 feet, 70 meters. In all the bluffs in which the formation is 
thus clearly exposed, one may see indistinct but definite stratification in 
beds that are usually several feet thick. The strata are not distinguished 
by a difference of composition, but appear to be defined by a horizontal 
parting in homogeneous material. Throughout the prevailing fine loess, 
which makes up the greater part of the formation, there are beds of 
gravel, the wash from the nearby hills. Near Huang-t’u-chai, a temple, 
which is said to have been built about 350 years ago, stands at a dis- 
tance of about 100 meters from the neighboring stream, on a bluff 80 
feet, 24 meters, in height. The cliff of loess has receded until the 
temple is in danger (illustration, atlas sheet B III) and we may assume 
that the building formerly was much further removed from the edge of 
the canyon. If we admit that at the time of its construction the bluff 
was near the present position of the river bed, we should have a max- 
imum retreat of 100 meters in 350 years. The time and distance in 
this estimate are both approximations, but they serve to give some idea 
