QUATERNARY. 185 
quence of a change from moist to arid climate, a deep layer of decayed 
rocks was denuded of vegetation and exposed to effects of winds and 
occasional rains.* The disintegrated material was transported and sorted, 
both by wind and water; wind being the more effective agent during the 
dry seasons and on wide plains; waters doing a larger work during rainy 
seasons and in river valleys. Sorted and transported repeatedly and 
alternately by winds and waters, the material came to consist in great part 
of fine dust, the loess, which both agents could carry in largest amount; 
but this was always mingled, as it is now, with some coarser sand and 
gravel introduced by flood waters. Beyond desert basins, the path along 
which the Huang-t’u was distributed was chiefly down the valleys of a 
previous physiographic epoch, as it is now down the valleys of the present 
far more mountainous surface. It was deposited on flood-plains and in 
lake basins. The lighter portions of it were blown out onto mountain 
slopes and gathered beneath wind eddies or in sheltered hollows. In 
course of distribution it became thoroughly decomposed and oxidized; 
and where it accumulated and was exposed to subaerial conditions it 
acquired vertical cleavage, a secondary characteristic due to gravity and 
movement of ground waters, and became charged with salts brought in 
by such waters. The processes of transportation and accumulation are 
in progress now and are believed to have been similar in past ages. 
DESCRIPTION OF LOCAL OCCURRENCES. 
The description of local occurrences of the Huang-t’u formation, 
which is in its general aspects monotonous, necessarily involves some 
repetition. Wherever seen, its general characteristics are its constitution, 
its vertical structure, and, in valleys or basins, its slightly concave surface. 
The particular features which distinguish one occurrence from another are 
the greater or less proportion of coarse wash in comparison with the pre- 
dominating constituent, the loess; or its occurrence in peculiar situations, 
where its presence is not readily attributable to the ordinary agents of 
deposition; and the presence or absence of stratification. 
In the following paragraphs the notable occurrences of Huang-t’u 
along our route are briefly described. 
The Huang-t’u formation constituting the Great Plain of eastern 
China is characterized in von Richthofen’s geological map as alluvial loess, 
and such it is to a great extent, inasmuch as it is the deposit from the 
waters of the Huang-ho, which has filled in the space between the mountains 
of Chi-li and Shan-si on the west and those of Shan-tung on the east, estab- 
lishing the seacoast far to the east of the position which it would otherwise 
*Pumpelly. Relations of Secular Rock Disintegration to Loess, Glacial Drift, and Rock Basins. 
American Journal Science and Arts, vol. 27, 1879. 
