LOESS OF CHINA—BARBOUR 295 
The principles involved are three—(1) continued abundant growth 
of steppe vegetation, especially course grass and bent; (2) contem- 
poraneous and steady supply of fine dust, which was carried into the 
region by the winds and settled down to the ground, where it was 
protected by the vegetation from further disturbance and became 
part of the permanent soil mantle; and (3) subsequent destruction 
of all traces of such preexisting vegetation under climatic and 
ground conditions that led to the almost complete oxidation of the 
organic matter. The principal factor in such destruction is appar- 
ently oft-repeated moistening followed by drying and access of fresh 
air, just as happens when rain waters percolate through the loose 
ground above the permanent water level in a region of moderate 
but frequent rains. 
This explanation suggested by Doctor Berkey tallies with ob- 
served fact in climatically analogous regions to-day. The dust 
which partially buries the standing blades of growing grass, con- 
solidates round them and tends to preserve the structure lines of the 
vegetation; it thus possesses from the outset the vertical lines of 
weakness that lead to the characteristic cleavage afterwards. 
With regard to the question of the removal of the evidence by 
ground conditions especially destructive to organic remains, it might 
be pointed out that the fossils habitually found in the loess are those 
capable of resisting such attack from ground water in the vadose 
zone, while all more delicate and unstable structures are wiped out; 
the Struthiolithus shell is frequently found in the loess, whereas not 
a single example of the bones of the bird itself is known to science. 
This explanation in the main reestablishes the picture of condi- 
tions given by von Richthofen and revives his vegetation theory so 
criticized by Kingsmill, Ward, and Willis, but with modifications, 
which, as far as can be ascertained, do not appear to have been put 
forward in exactly this form by any other student of the problem. 
“HUANG T’U” AND “LOHSS ” 
Willis in his researches gives the formation name “huang t’u” 
to the entire series which is now recognized as including the red 
clay, the true loess, and the gravels with “redeposited loess.” This is 
also the broader sense in which the word “ loess” is constantly used 
to-day.*® It is true that such observers may fully recognize the in- 
clusion under this term of deposits of both stratified and unstratified 
material, and Willis, for example, states that the age “ranges from 
late Pliocene or early Pleistocene to the present, it (the huang-t’w) 
having been continuously in process of deposition throughout the 
Quaternary and possibly since a prequaternary date.” But it has 
16K. G., Sowerby (2-116). 
