250 RESEARCH IN CHINA. 
Von Richthofen says:* 
One of the consequences of the vertical arrangement of capillary texture is that 
the loess takes up water like a sponge. The heaviest rains leave only slight traces upon 
the surface, therefore no puddles remain standing; and for the same reason there are, 
in the true loess deposits, no lakes. I never saw a spring flow from it; they first occur 
in number there where the loess rests upon the hard rock. 
Coming in contact with a dry mass of loess, underground waters 
should be energetically absorbed and carried upward by capillary attrac- 
tion. Being the run-off of larger or smaller areas of steep mountain slopes, 
and being subject, in their subterranean position, to the major changes 
of seasons only, they should be more copious and more constant than the 
waters entering at the surface of the Huang-t’u. We may thus consider 
the dry mass as becoming charged with moisture from both above and 
below, but in larger degree from below. If sufficient moisture be supplied 
the two moistened parts would meet and the whole mass become damp. 
The ground water, thus entering the Huang-t’u, carries with it a 
proportion of salts derived from the rocks. In northwestern China the 
bed-rock over very large areas is limestone, and the Huang-t’u is known to 
contain large amounts of carbonate of lime, both as a generally distributed 
constituent and in nodules. Concentration from ground water occurs in 
soils as a result of evaporation and through absorption and chemical 
reaction. The conditions can only be suggested here. For a fuller account 
the reader is referred to articles by Way,t Warington,{ and Van Bemme- 
len.§ From their experiments it follows that the inorganic colloids, such 
as silicates of iron and alumina, absorb the alkaline earths and alkalies 
from salt solutions (chlorides, nitrates, and sulphates) in exchange for 
the base of the colloid. Hydroxide of iron absorbs soluble salts in conse- 
quence of their diffusion in the water which it contains. Colloid silica 
takes alkali from alkaline solutions of carbonates and also lime from car- 
bonate of lime. The presence of carbonate of lime promotes the decom- 
position of potash salts with the formation of a lime salt with the acid 
and the absorption of potassium hydrate by the silica. ‘The Huang-t’u 
formation being made up of the silicates of iron and alumina, hydroxide 
of iron, and silica, all of which are probably present in large amounts as 
colloids, the conditions for these reactions are favorable and the formation 

* China, vol. 1, p. 58. ‘‘Eine der Folgen der senkrecht angeordneten capillaren Textur besteht 
darin, dass der Léss Wasser aufsaugt wie ein Schwamm, Die starksten Regengiisse lassen nur geringe 
Spiiren auf seiner Oberflache. Es bleiben daher keine Tiimpel stehen, und aus demselben Grund gibt 
es auch auf eigentlichem Léssboden keine Seen. Quellen sah ich nie in ihm entspringen; sie treten erst 
dort in Menge hervor, wo der Léss dem festen Gestein auflagert.” 
{ Way. Journal Royal Agricultural Society of England, vol. x1, p. 313, and vol. xi, p. 123. 
t Warington. Journal Chemical Society of London, vol. xxi, p. 1, 1868. 
§ Van Bemmelen. Zeitschrift fiir anorganische Chemie, vol. xx1m, pp. 358-364, and vol. XLII, p 314. 
