102 Kansas Academy of Science. 



seolian class, and to search diligently for criteria of discrim- 

 ination between the two. 



On the same subject Leverett says:' "The mode of deposi- 

 tion of the loess still remains one of the most puzzling prob- 

 lems of Pleistocene geology. . Both the seolian and aqueous 

 hypotheses have strong adherents. Among the students of 

 the Mississippi valley portion, however, all grant that the in- 

 fluence of wind has been important; and probably all would 

 concede that water had been influential. The division of opin- 

 ion, therefore, is concerned with the relative importance of 

 wind and water in the distribution of the loess. Mr. Udden, 

 after a careful examination, has decided that a large part of 

 the loess may have been deposited through the influence of 

 the atmosphere as an agent of erosion, transportation, and 

 sedimentation. Mr. Chamberlin says, on this point, that the 

 loess of the Mississippi valley was in some way connected with 

 the great streams of the region. The abrupt border of the 

 loess at the edge of the lowan drift-sheet, both in Illinois and 

 in Iowa, gives it a more or less direct genetic relationship with 

 the ice. The gradation of the loess into glacial clays further 

 tends to conform the association of the loess with glacial ac- 

 tion. The influence of glacial action is also shown in the 

 presence of silicates, which are decomposable under prolonged 

 weathering, and of calcium and magnesian carbonates, none 

 of which can be supposed to be from residuary clays. The 

 loess seems to have been formed by glacio-fluvial action, he 

 (Chamberlin) assuming (a) the presence of the ice-sheet at 

 the chief stage of deposition; (b) a very low slope of land 

 and consequent wide-wandering glacial rivers; (c) the devel- 

 opment of extensive flats over which the silts were spread; 

 (d) great periodic extension of glacial waters caused (1) by 

 periods of warm weather in the melting season, and (2) by 

 warm rains. Upon the retreat of the waters, he concludes, 

 extensive silt-covered flats would become exposed to the 

 sweeping influence of the wind ; and when dried the silt would 

 be borne in great quantities over the adjacent uplands. Thus 

 were formed the seolian loess, the aqueous loess having been 

 formed by the first process above mentioned. Again, he says : 

 "While individual types of both deposits (seolian and aqueous) 

 are not difficult to find, a criteria or series of criteria of gen- 



9. G. S. Mon. xxxviii, p. 177. 



