THE LOESS OF CHINA. i 
self-fertilizing power. It is, in itself, an unstratified, even-textured, yellowish or 
yellowish-brown earth of very fine grain. It consists largely of exceedingly fine 
particles of silica with an admixture of equally finely comminuted silicates, some 
oxide of iron, and a varying amount of calcareous material which often segregates 
into concretions of irregular form. It generally contains also various soluble salts 
of the alkaline earths and alkalis. While it will maintain vertical cliffs apparently 
for centuries in a dry climate, in which the dwellings of whole villages are exca- 
vated, it can be crumbied between the fingers. It is rendered porous by innumer- 
able tubular channels left by the decayed stalks and roots of grasses, and roots of 
trees may penetrate it to a depth of 100 feet or more. 
Loess has played, and still plays, such an important part in the history of man 
that I shall devote several paragraphs to a description of the manner in which it is 
formed, and I do so not only because of its importance in connection with the 
past history of Turkestan, but also because of its general interest. 
The most striking illustration is offered by northern China, where it covers 
a great part of the surface, both on the hills and on the lowlands. Its fertility 
seems to be inexhaustible, a quality it owes partly, as Richthofen remarks, to its 
depth and texture, partly to the salts brought to the surface after rains by capil- 
lary attraction acting through the tubular channels left after the decay of succes- 
sive generations of the grass stems inclosed during its accumulation, and partly 
to the increment of fresh dust that is still brought by winds from the interior. 
Its self-fertilizing ability is shown by the fact that crops have been raised continu- 
ously, through several thousand years, on its immense areas in China, and practi- 
cally without fertilizing additions. It is on these lands that dense populations 
accumulate and grow up to the limit of its great life-supporting capacity, the only 
check being in the fact that in this region of light rainfall, a drought lasting through 
several successive years produces at times famines that may exterminate many 
millions of people. 
China offers, too, another striking illustration of the influence of this remark- 
able soil on the history of its fortunate possessors. At repeated intervals of a few 
centuries, its population has been decimated and over large areas almost annihi- 
lated by overwhelming invaders or by civil wars, as in the Tai-Ping rebellion of 
the past century. In southern China, where there is no loess, the area that can 
be cultivated is absolutely dependent on the amount of available fertilizers, and 
since the population is so dense and the holdings are too small to admit of the 
keeping of live stock, the only available fertilizer is that produced by man. The 
result of this is that population recuperates rapidly in the loess-covered provinces 
where cultivation is dependent only on the ability to prepare the soil and to plant 
the seed; while in the south the ability to support population waits on the slow 
increase of fertilizing humanity. 
Again, great events in our own history are directly connected with the distri- 
bution of this wind-borne soil—events which have shifted and radically changed 
the populations of Europe and have caused the downfall of empires and replaced 
civilizations by semi-barbarism. For from north of the Caspian to Austria extends 
