PHYSIOGRAPHY OF NORTHWESTERN CHINA. 251 
may become charged with the salts taken from ground waters which rise 
by capillary attraction within the mass. When the waters fluctuate in 
consequence of periods of dryness, the salts in the colloids would remain 
and an additional amount would be deposited by evaporation. 
The distribution of the loess-mannchen, or calcareous nodules, bears 
on the conditions of deposition from ground water. The nodules occur 
in horizontal layers, with their longer axes vertical. Von Richthofen says: 
Only the loess-mannchen are arranged in special horizontal layers. If, however, 
one examines such an apparent bedding plane, it appears that all these concretions stand 
with their longer axes vertical. They must, therefore, have developed in the place and 
position in which they are found.* 
In alkali soils which become saturated with ground water and suffer 
evaporation, a continuous layer of hard calcareous deposit commonly 
results. The loess-mannchen, being discrete and widely distributed, appear 
to have segregated under conditions of less complete saturation of the 
porous mass. It is conceived that they represent centers of aggregation, 
set up at appropriate intervals in horizontal spacing and built up and 
down vertically according to the control of capillarity, of gravity, and 
oscillations of the surface of moisture. 
That the ground water in the Huang-t’u generally falls short of satu- 
ration is rendered probable by the behavior of loess in contact with abun- 
dant water. It puddles readily, becomes practically liquid, and flows en 
masse, leaving a vertical well or tunnel if the wet loess be surrounded by 
dry. ‘This capacity to flow is due, as has been stated to me by Prof. C. S. 
Slichter, to the fact that any solid particle, whose diameter is less than 
the thickness of a capillary film of water, may enter that film and, becoming 
part of the liquid, flow with it. Were a body of loess to become sufficiently 
saturated with water it would be transformed into a liquid mud, which 
could not possibly remain in many of the situations in which it is found. 
An instance of a landslide, which we may attribute to saturation of the 
loess, was observed about 4 miles, 6.5 kilometers, east of Hua-chéu, Shen-si, 
at the base of the Ta-hua-shan. For three-fourths of a mile, 1 kilometer, 
parallel to the front of the mountains and out to 2 miles, 3 kilometers, 
from their base the level plain was covered with low irregular mounds of 
loess and angular rock masses. The latter were from to to 15 feet, 4.5 
meters, in diameter and were imbedded in fine loess above the general 
level of the plain. Among the hillocks were marshy hollows. The moun- 
tain slope opposite this occurrence was bare of the loess, which elsewhere 
* Von Richthofen, China, vol. 1. p. 61. ‘‘Nur die Léssmannchen sind in besonderen horizontalen 
Lagen angeordnet. Untersucht man jedoch eine solche scheinbare Schicht, so zeigt es sich, dass alle 
diese Knauern mit ihren Langsaxen senkrecht gestellt sind. Sie miissen daher an Ort und Stelle ent- 
standen sein.’’ 
