358 NATURAL HISTORY BULLETIN. 



cerning the correlation of loess and Iowan drift largely upon 

 the conclusions drawn by McGee, Calvin, and other Iowa 

 geologists who were investigating special problems in com- 

 paratively restricted areas. McGee's discussion* of the cor- 

 relation of loess and the Upper Till, now known as the Iowan, 

 is so positive, and the numerous examples which he cites seem 

 to be so conclusive, that it is not strange that most students 

 of pleistocene geology accept his conclusions. That Leverett 

 did so is evident from his statements"!" that "this sheet of loess 

 seems to be intimately connected with the Iowan drift sheet, 

 as shown by McGee, a relation while subsequent investigators 

 fully confirm." The latter were chiefly members of the Iowa 

 Geological Survey. 



McGee correlated these tw 7 o deposits chiefly because he 

 often failed to find a sharp line of demarkation between them. 

 On p. 442, 1. c, he says: "The northern loess is never with- 

 out a basal pebbly layer or sand bed ..." and he includes this 

 in the loess series. In the subsequent discussion of the 

 southern loess, pp. 442-6, he includes a sandy or pebbly layer 

 capping the Upper Till (Iowan drift) with loess. In the dis- 

 cussion of the "loess of the river ridges and paha," on pp. 

 454) 455, 459 and 460, he refers sands and gravel to loess. 

 The same is true of his "southern loess," on pp. 462, 466, 467, 

 etc., though here he finds the loess grading directly into drift 

 clays. 



The reference of these underlying deposits to loess is evi- 

 dently erroneous. X McGee himself recognized the fact that 

 loess is usually readily identified. § 



The only reason, so far as appears from his discussion, which 

 he had for including some of the basal sands and gravels in 



*llth An. Rep. U. S. Geol. Sur. 



tOn p. 25 of the monograph on the Illinoisan Glacial Lohe. 

 + Leverett makes the same error in the monograph of the Illinoisan 

 Glacial Lobe, p. 157, etc. 

 §See pp. 292-3, etc., 1. c. 



