R. Pumpelly—Secular Rock-disintegration. 143 
dry land, and has been covered by abundant vegetation, to be 
transformed into a dry, central area. The destruction of the 
protecting plants would expose to the fierce winds the loose 
residua of long periods of disintegration of the rocks. Under 
this process of a dry separation the material would be sorted, 
the finest carried to great distances, would find resting places 
only where under the protection of steppe grasses it could be 
fixed and transformed into loess. The coarsest would remain 
nance nor of being fixed, would drift in dune-like waves before 
the prevailing winds, transforming everything in its track into 
desert wastes. 
- We have in the immense loess deposits of China, often more 
than one thousand feet thick, and in those of wee and west 
of the Mississippi, which are often measured by hundreds of 
feet, the best evidence of the ability of the loess-forming pro- 
cess to accumulate vast masses of fine material in a compara- 
tively short time. 
products of wave-erosion, are now continuously deluged with 
yellow silt, 
The great silt-loaded rivers of the world are, in at least nearly 
all instances, streams which after running clear water for en 
ages, are now merely temporarily employed in making a rapid 
ransfer of the loess which is itself the product of a concentra- 
tion by wind of the products of a slow disintegration which 
may have lasted from the Carboniferous period to the Post Ter- 
tiary. 
hen we consider not only the enormous volume of this silt, 
but also the fact that its extreme fineness causes it to be car- 
ried over great areas in suspension before it sinks, we can con- 
ceive that its effects may be catastrophic as regards the less 
plastic forms of life. This would be the case especially where 
