3/8 The Loess of North America. [May, 



Richthofen holds 1 that the loess is a subaerial accumulation, 

 due to the drifting action of the winds ; to transportation by riv- 

 ulets from the hills immediately adjacent to each loess basin ; and 

 to the mineral material left over the basin by the growing grasses 

 and other plants. The material for wind transportation is gath- 

 ered from the circumjacent or even from remote rocks which 

 were decomposed or disintegrated by alternate changes in tem- 

 perature or humidity. The plants that covered the great plains 

 served to stop the wind-drifted particles, and thus kept the accu- 

 mulation ever in progress. Observing certain local differences in 

 the appearance of the deposits which he studied, he invented the 

 distinctions of land-loess and lake-loess. The last named was de- 

 signed to account for certain indications of stratification or lamel- 

 lation not to be adequately explained by the wind theory.- The 

 present system of drainage he accounts for much as do most 

 other geologists, the main difference consisting in the assumption 

 of great changes of climate causing heavy rains which led to 

 floods. The usual indication of changes of level are also 

 noticed by him, but they seem to have led to novel inter- 

 pretation. Von Richthofen states that he found no evidence 

 of a fresh-water fauna in the formations he studied, but land 

 forms of molluscous and other animals abounded. In this 

 he is directly opposed by the earlier an 

 of Pumpelly 3 who distinctly states tha 





large rivers which must have 





and independently of the fac 





On p. 43 he derives the fo 



all the information we posses 







were penned eleven years l,e 



