ft. Pumpelly—Secular Rock-disintegration. 135 
remark here that Richthofen has made known the fact that the 
they are self-fertilizing. This he ascribes partly to the porosity 
of the material which causes it to absorb carbonic acid and 
ammonia in large amounts from the air; but more especially to 
the elevation of nutritive salts in the capillary tubes by diffu- 
sion whenever a rain establishes a moist communication between 
the surface and the saline water below the drainage level. 
Thus, whenever climatal changes have restored more or less 
moisture to the atmosphere of a loess district, we have in it the 
utmost fertility. The cold and elevated regions of northern 
China are the granary of the empire—and the seat of the pres- 
ent great famine. 
Attention has been recently called by the German geologists 
to the great fertility of the European loess, and Professor Hay- 
den has emphasized the fact that the abundant productiveness 
of much of the West is due to the same soil. 
Recognizing from personal observation the full identity of 
character of the loess of northern China, Europe and the Mis- 
souri Valley, I am obliged to reject my own explanation of the 
origin of the Chinese deposits, and to believe with Richthofen 
that the true loess, wherever it occurs, is a sub-aerial deposit, 
formed in a dry central region, and that it owes its structure to 
the formative influence of a steppe vegetation. ; 
The one weak point of Richthofen’s theory is in the evident 
inadequacy of the current disintegration as a source of material. 
‘hen we consider the immense area covered by lcess to 
and again that the accumulation represents only a very short 
region. Where the streams sink away, or where the lakes 
which receive them have dried up, the finer products of the 
erosion of a -large territory are left to be removed in cust 
storms. 
_ I. The second, and I believe, the more important source is 
in the residuary products of a secular disintegration which we 
will now consider. 
In all regions where the soil is protected by a luxuriant vege- 
tation the greater part of the insoluble products of disintegra- 
