LOESS OF CHINA——BARBOUR 285 
Sample 2: Per cent 
(@)Pereentage of sand and silt by settling»= + -+2--2+-=+-=-++-+ 81. 70 
Pereentaee iol Clayoem 2 = 5. ate ee ee ee ke he 18.3 
100. 00 
(b) Micrometer study: ; 
Class Average diameter of particle 
LM GO CCM Fete h cls ee Me oe ens ee 2 ee ee 0.10 millimeter 1.00 
Very finer Sandee te aes oe .063 millimeter 25, 00 
S11 ip ca AE ISS Lh A SR a ee .030 millimeter 54, 00 
MOU ee te en ne ne ee a .004 millimeter 20.00 
100. 00 
SOIL CHARACTERISTICS OF LOESS 
Reasoning a priort from the mineralogical and chemical analyses 
above, it might be expected that loess would differ in several respects 
from normal river silts of corresponding texture. These latter, 
owing their fineness to prolonged wearing down by stream action, 
and exposure to the attack of chemical weathering, tend to form 
products of relatively stable composition (especially silica, ferric 
' hydroxide, and clay), from which the more soluble elements have 
been removed. Such clayey soils let water permeate only with difh- 
culty, are sticky and heavy to till, and may call for fertilization by 
the addition of those chemical elements desirable for plant growth, 
which have been gradually leached out by the solvent action of 
' water. In these points Chinese loess shows a strong contrast. The 
analysis above is of special interest in showing how fresh and unde- 
composed much of the material of true loess may be, the minerals 
being those commonly found predominating in ordinary unweathered 
granite and allied rocks, and appearing actually almost less affected 
by alteration than the weathered surface of any average rock. It 
may be said here in anticipation that this seems to form additional 
evidence in favor of the now generally accepted belief that such 
loess is, in the main, a wind-blown deposit formed under arid or 
steppe conditions. 
There is as yet a dearth of quantitative data as to the favorable- 
ness of loess as a soil. No information could be obtained as to the 
extent to which cropping of the soil in China through past years 
with the soya bean and other legumes has enriched (or impover- 
ished) it, especially in the matter of nitrogenous compounds, though 
there is no question that farmers have discovered experimentally 
through centuries of practice the penalties of nonrotation of crops; 
this knowledge and the universal practice’ of manure fertilization 
makes it hard to isolate the results due to any one factor. Certain 
generalizations, however, are possible, particularly where based upon 
experience of loess soils in other countries. Lyon and Buckman state, 
20837—27——-20 
