140 X. H, WINCHELL — WAS MAN IX AMEKlCA IN GLACIAL PERIOD 



gists until the hypothesis of Richthofen, which assigns an eolic origin 

 to the loess of China, accepted, as it was, and reinforced by Professor R. 

 Pumpelly. At the present time a few geologists accept the eolian 

 tlieor}', and almost wholly explain the phenomena of the loess by that 

 theory. A few others admit a modified and subsidiary agenc}' due to 

 wind cooperating with water and somewhat changing the original mass, 

 while a considerable number, who are those not directl}" concerned and 

 who constitute probably the larger half of the geologists of the United 

 States, do not have positive convictions, but prefer to maintain a recep- 

 tive attitude while waiting for the demonstration of either the eolian or 

 the aqueous hypothesis. The discussion is becoming acute. Some of 

 the principles and the facts that are put forward are so plainh^ stated 

 that it is possible to consider them without danger of misconception. 

 The aqueous hypothesis requires the following : 



1. That the whole mass be water-deposited. 



2. That it shall have once filled the vallej^s of the streams whose 

 blufis it forms nearly or quite to the tops of those bluffs, the present 

 immediate river valleys having been excavated in the loess since its 

 deposition through the erosive and transporting action of the rivers 

 themselves. 



3. That the main body of the loess is contemporar}^ with an ice epoch, 

 now known to be the lowan stage of glaciation, 



4. That the loess-forming conditions required a low-lying attitude of 

 the regions where it was formed, resulting in slow drainage, enlarged 

 rivers, many lakes, vast swamps, and mud flats. 



5. To this should be added, as a later proved corollary of the aqueous 

 hypothesis, that the loess is not everywhere the same, either in compo- 

 sition or in structure, but depends on local conditions, and that it passes 

 both horizontally and vertically into glacier-laid deposits. 



The eolian hypothesis requires the following : 



1. That the loess was transported by winds and deposited where it is 

 found. 



2. Tliat it originated in the western plains, or on the dried bottom 

 lands of the great rivers, and by the prevailing western winds was carried 

 into the valleys, or more especially onto the immediate bluff's of the 

 main rivers. 



3. That the valleys were never filled with it, but, on the contrary, the 

 resultant eff'ect of the winds has been to keep it out of the immediate 

 valleys through the powerful action of high winds in raising dust storms 

 along the dried flood plains. 



