: 
OT ce AL SE Oy SM Sy So a Meee te aE Se N R ST, De ee ee REE SM Rc a es 
Re. Pumpelly—Secular Rock-disintegration. 138 
Art. XVI.—The Relation of Secular Rock-disintegration to Less, 
Glacial Drijtand Rock Basins ;* by RAPHAEL PUMPELLY. 
THE recent volume of Baron Richthofen’s great work on 
China and Central Asia, is, to a considerable extent, occupied 
with a description of the great loess formation and of the pro- 
cesses to which it owes its origin. 
This remarkable formation covers several hundred thousand 
square miles in northern China, and larger areas in the rest of 
Asia. It forms the soil also over an immense area in the 
western United States. Its thickness varies, in China up to 
2000 feet, and to 150 and 200 feet in Europe and America. 
Loess is a calcareous loam. It is easily crushed in the hand 
to an almost impalpable powder, and yet its consistency is 
such that it will support itself for many years in vertical cliffs 
200 feet high. A close examination shows that it is filled with 
tubular pores branching downward like rootlets, and that these 
tubes are lined with carbonate of lime. It is to these that it 
This remarkable combination of softness with great strength 
i i el 
To the same qualities is due the fact that the leess districts 
_ of China are exceedingly fertile plains, in each of which a 
_ Tapidly progressing erosion has excavated the most labyrinthine 
: valley systems, in which all the members, down to the smallest 
tributaries, are sunk with vertical walls to depths of from one 
_* Read before the National Academy of Science, April 10th, 1878. 
