186 RESEARCH IN CHINA. 
occupy under existing conditions of the altitude of the land. This alluvial 
deposit differs from ordinary river mud in that it consists chiefly of fine 
wind-sorted loess. We should not, however, too hastily infer that it has 
been brought to its present position by wind. On the contrary, the posi- 
tion of the flood-plain with reference to the relatively high river channels, 
and the obvious genetic relation existing between the silt-burdened rivers 
and the far-spreading plain demonstrate clearly that the deposit owes its 
distribution chiefly to muddy waters, which have built a very broad and 
very flat alluvial cone. The constitution of the Huang-t’u in this district 
is due to conditions ina remote region, from which it has been brought by 
the usual agents of transportation, the rivers. Nevertheless, the activity of 
winds is effective under existing climatic conditions, in consequence of which 
the plain is exposed without any covering of vegetation or snow during 
nearly half of each year. The fine loess, which was elsewhere sorted from 
the coarser constituents with which it originated, and which is here mingled 
with obdurate quartzose river sand, is separated from the latter by the 
action of the wind and sweeps in dust clouds over the plain. ‘The sand, 
thus cleaned, remains to constitute sandy stretches and form dunes. The 
details of the distribution of these products of wind action are described for 
the Bay of Peking, in the chapter on artesian water supplies. The stretches 
of sand are usually adjacent to river courses, from which it is blown out 
by the prevailing winds, while the migrating dust clouds settle anywhere 
without reference to features of the surface, except in so far as the latter 
afford a lee or induce an eddy in the winds. About the hills there are 
usually places which offer shelter to the wind-blown dust and in which it 
accumulates in drifts. Where a range of hills extends for some distance 
across the current of a prevailing wind, the crest induces an eddy on the 
windward slope and the lower part of the hills becomes covered with loess 
up to a gently concave surface, which is that on which the scouring effect 
of the wind balances the tendency to deposition. This form of deposit 
is common throughout the mountainous regions occupied by the Huang-t’u, 
and the drifts of loess on the windward slopes are sometimes of notable 
thickness. Similar drifts may be found in valleys on the lee side of a range, 
but, contrary to what one might expect, they do not seem to be as deep 
or as extensive as those in concavities to windward. 
We observed the alluvial Huang-t’u formation of the plain and its 
wind-derived products in Shan-tung about the margins of the peninsula, 
and in Chi-li en route from Pau-ting-fu to Ning-shan. A special study 
was made in the Bay of Peking, and it was there that the dominant im- 
portance of the rivers as the chief agents of distribution of the formation 
was first recognized. 
