576 E. HUXTIXGTOX SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



northern China this material has been accumulating for ages and is still 

 in rapid process of deposition. There can be no question as to its origin. 

 I have myself seen loess blown from the Takla Makan Desert of the Tarim 

 Basin and deposited on the northern flank of the Kwen-lun Mountains, 

 8,000 feet above the desert and 60 miles away. Standing on the moun- 

 tain side in the early morning, we could see the desert clearly. Gradually 

 it became obscured by dust, under the influence of a strong north wind. 

 By afternoon the dust reached us. It fell so thickly that our writing 

 paper became covered with it and had to be brushed every few minutes 

 to prevent the pen from blotting. Conditions like this seem to be the 

 only ones where any great quantity of loess is being deposited at the 

 present time. Xevertheless, as is seen in figure 20, there are large areas 

 where vast deposits were formed during Pleistocene times, but which 

 now are not in such relation to deserts that they could possibly receive 

 dust from them. A belt of this sort extends across the southern borders of 

 Siberia between 45° and 50° north. Its westAvard extension passes through 

 southern Eussia, across Eoumania and Hungary, up the Danube, and 

 over into France. There it extends as far as Brittany and even over into 

 the extreme south of England. Other small areas of loess lie in southern 

 France near the mouth of the Ehone and in southern Spain. In America 

 similar conditions prevail. The central part of the United States, espe- 

 cially along the Missouri, Mississippi, and Ohio rivers, contains abundant 

 deposits of loess dating from the Glacial period. Thus, although as a 

 general rule it appears that in modern times all known deposition of loess 

 on a large scale is due to winds blowing from deserts, yet in ancient — 

 that is. Pleistocene — times the deposition of loess seems to have been 

 closely associated with glaciation and to have taken place chiefly not far 

 from the front of the ice. The ice indicates heavy precipitation or else 

 low temi^erature and the consequent absence of rapid melting and evap- 

 oration. The loess indicates lack of precipitation or else high tempera- 

 ture and extremely rapid evaporation. 



The peculiar juxtaposition of these two phenomena has been one of 

 the most puzzling features of glacial geology. It has led to the theory 

 of a twofold. origin of loess. Geologists have been forced to conclude that 

 this material can originate not only in deserts, but also in the outwash 

 plains which lie in front of glaciers. It has been supposed that during 

 the Pleistocene summer the ice melted rapidly and great streams flowed 

 from its front. The streams must have spread into many channels and 

 flooded large areas. During the winter, when melting ceased, the streams 

 presumably diminished or even disappeared in many cases. Then the 



