PHYSIOGRAPHY OF SOUTHERN SHEN-SI. 329 
The basin is apparently a widening of the river valley, which might 
readily be attributed to the softness of the sericitic schists in which it is 
excavated. Certainly it is probable that the weakness of the rock has pro- 
moted the widening, but it hardly seems to suffice to explain all the facts, 
as the same schists form the hills where we crossed them on the south- 
west. The direction of the longer axis, which is nearly at right angles to 
the course of the river, the gentle slopes which sink toward the basin, and 
its peculiar situation among high ranges suggest that it is an oval down- 
warp modified by erosion. 
The river flows across it in a gravelly channel above bed-rock, and is 
faced on the north opposite the city by bluffs of gravel about 120 feet 
high, to a level surface. The southern margin of this deposit, which 
occupies a large area in the basin and which once undoubtedly filled it, at 
least to the top of the bluff, was crossed near the 1,100-foot contour 3 miles, 
5 kilometers, southeast of the city. The deposit consists of river gravel 
and shingle, with pebbles up to 15 inches, 38 centimeters, in diameter and 
occasional beds of sand. ‘The stratification is essentially horizontal and 
the strata are cross-stratified in various directions. The pebbles represent 
all the varieties of schist, argillite, quartzite, granite, and basic intrusives, 
which we observed along the Han. All those rocks which are liable to 
decay are thoroughly decomposed, only quartzite and siliceous argillite 
remaining sound. The pick was easily driven through the largest granite 
cobble. Thus it seems probable that the deposits are not of the latest 
Pleistocene age, but older. We call this deposit the Hing-an gravels. 
In the valley southeast of Hing-an-fu we found a rock-cut terrace 
at the 1,100-foot contour, corresponding with the upper limit of the 
Hing-an gravels. Thus it is apparent that some condition determined 
lateral corrasion by the stream when at that level, and the suggestion 
lies near that the gravels accumulated as delta deposits in a body of water 
confined among the hills. In the light of present knowledge it is equally 
possible that the surface of the gravel deposit formed for a time the local 
base-level to which the streams cut. 
From the Han to the Nan-kiang, southeast of Huang-yang-p’u, our 
route followed the valley of a brook in a little canyon 80 to 120 feet deep 
which wound about so constantly that the view was limited to a hundred 
yards or so ahead. Each of the little bends partially inclosed a remnant 
of the valley floor on which the brook had assumed its meandering course 
and which correspond to the surface of the Hing-an gravel. 
On ascending to the ridge above Lau-hién, at an altitude of 2,200 feet, 
670 meters, above sea, we looked northward over the old valley surface, 
which had been recognized in the view of the Han valley near Siau-tau-ho. 
