360 NATURAL HISTORY BULLETIN. 



In cases where drift underlies the loess, and once formed 

 the land-surfaces, the gradual accumulation of soil upon plant- 

 covered areas would usually result in such blending as may 

 sometimes be observed between the drift and loess. 



This blending, therefore, does not prove a common origin, 

 and McGee's lowest member of the loess series, that including 

 sand and pebbles, should be excluded from the loess. It seems 

 to be made up, in part, of residual sands and gravels, such as 

 in places cap every drift-sheet in Iowa, and evidently repre- 

 sents the product of post-glacial action upon superficial por- 

 tions of the underlying drift, and, in part, of gumbo which quite 

 generally overlies the Kansan drift, and probably also repre- 

 sents post-glacial modifications of old drift surfaces. It is evi- 

 dent that but for the occasional blending here discussed, McGee 

 himself would have separated this member from his series, for, 

 speaking of the pebbly and sand)- layer, on p. 442, 1. c, he 

 says: "This structure is so unlike the mass of the loess, and so 

 like the upper drift sheet in composition and texture, that in 

 a taxonomy based on these characters it might with propriety 

 be classed with the latter deposit." 



The writer has made a personal examination of the majority 

 of the sections reported by McGee to prove the intergradation 

 of loess and drift, and has also been able to examine other sec- 

 tions in the same territory.* Reference to McGee's work, pp. 

 464-5, 1. c, shows that most of the sections cited are situated 

 in the southwestern part of Johnson county, and in Iowa 

 county, and that in connection with but one of these, is it 

 specifically stated that the fossils extended beneath the pebbly 

 layer, namely the well-section in sec. 15, T. 79 N., R. 7 W. 

 For obvious reasons this section could not be examined, but 

 in no other one of the many sections examined in that part of 

 the county, were fossils found beneath the upper line of peb- 

 ble-bearing clay. The fact is the loess does not blend with 



*In a paper now in preparation, the writer will give the exact loca- 

 tion of all the significant sections which were examined in this terri- 

 tory. 



