LOESS OF CHINA—-BARBOUR 287 
dition, especially as regards the presence of lime and other soluble 
mineral material available for plant nourishment. 
Both of these characteristics could naturally be explained as result- 
ing directly from an aeolian mode of accumulation, since the mineral 
decomposition occurring during transport by wind is almost neg- 
ligible in comparison with that due to prolonged water action. But 
before discussing the origin and age of the Chinese loess it is advis- 
able to refer again to deposits of loess in other parts of the world 
and to those other formations in China whose similarity has led to 
their being mistaken for it. 
THE LOESS OF EUROPE AND AMERICA 
In most respects the descriptions of Chinese loess could be applied 
equally to that of Europe and America. The same features call 
for special explanation—the fine texture and angularity of the par- 
ticles and the vertical cleavage responsible for the perpendicular cliffs 
and canyon walls. But in these countries there is in many localities 
distinct horizontal bedding, suggesting water action. A rough strati- 
fication is found also in the loess-carrying deposits which overlie 
the general loess in China, but these formations belong to a period 
of time, distinct and definitely later than the loess, which is not the 
case with the European and American stratified loess. 
In these countries it was recognized at an early date that loess 
had a complex origin different from that of the fine-grained silts 
made by river erosion. Of the other natural forces capable of pro- 
ducing quantities of “rock flour” of such fineness, explosive erup- 
tions yielding vast amounts of volcanic dust may be ruled out at once; 
the distribution, age, chemical and physical analyses, and habit of 
loess are against such an origin. On the other hand glacial boulder 
clay invariably contains a large amount of powdered rock material 
that has been crushed into minute sharp-cornered fragments; in 
Switzerland to-day the water of many Alpine streams is made 
whitish by the presence of much rock powder so fine as to be wholly 
inpalpable. But this water-borne “ rock flour ” is normally deposited 
in layers on lake bottoms or swept down to the sea. An equally fine 
powdery dust fills the air in, desert sandstorms.’ 
It is significant that the European and American loess belts lie 
along the line marking the glacier front of the Great Ice Age, or in 
adjoining areas into which it might have been carried by streams or 
wind. The vertical cleavage and general absence of stratification in 
loess has led to the belief that in Europe and America wind played 
a major part in distributing the rock dust originally powdered by 
the grinding action of glaciers. However, it is equally certain that 
7Walther, Denudation in der Wuste, Leipzig (p. 566 and 581). 
