THE LOESS AND THE LANSING MAN. 339 



the fine loess dust and spread it far and wide over the inter- 

 fluvial higher lands." Unfortunately the interfluvial lands 

 are often lower than the loess ridges along the streams. As 

 the loess recedes from the streams it usually becomes thinner 

 and its materials finer, both of which facts can probably be 

 accounted for by the greater distance from the source of sup- 

 ply of the material, — the bars of the streams. He further 

 states that "In these great areas of eolian loess only terrestrial 

 shells are found." As a matter of fact most of the loess re- 

 mote from streams (the "upland loess") is non-fossiliferous. 

 However, where fossils do occur they are chiefly, or wholly, 

 terrestrial. But so are the fossils from Natchez and Council 

 Bluffs; so are the fossils of by far the greater part of the loess 

 wherever it is found. No line of demarkation, vertical or 

 horizontal, can be drawn between two such divisions of the 

 loess. There certainly is nothing known at present to indi- 

 cate genetic differences. 



Hershey (1. c.) attempted to separate the upland non-fossil- 

 iferous loess from that which is fossiliferous, but the presence 

 or absence of fossils does not prove difference in origin. This 

 point has already been sufficiently discussed by the writer.* 

 Neither differences in altitude nor differences in fossils offer 

 satisfactory characters for a division of the loess, for both fail 

 when subjected to the only reliable test, — namely, applica- 

 tion in the field. 



Differences in composition and texture may frequently be 

 observed in the loess. It is evident that not all loess is of the 

 same age as measured with reference to the several drift sheets 

 which have extended southward into the latitude of Iowa. 

 The deposition of loess has continued through all the inter- 

 vals of the ice age. In the more northerly regions (i. e. Iowa, 

 etc.) over which the several ice-sheets passed, there were more 

 or less sharply defined differences between different portions 

 of the loess. Such differences have been observed by Todd 



*The Distribution of Loess Fossils, Proc. la. Acad. Sci., vol. vi, pp. 

 98-103, 1899; Jour, of Geol., vol. vii, March, 1899. 



