408 



GEOLOGY. 



that at all others, both in volume and areal extent. The loess deposited 

 at this stage is often referred to as " the loess/' and is usually cor- 

 related in time with the Iowan drift, though the strict accuracy of this 

 correlation has been questioned. It is at least later than the Kansan 

 and Illinoian sheets of drift which it mantles, and earlier than the 

 Early Wisconsin which overlies it. Locally, a thin mantle of loess 

 overlies the older part of the Early Wisconsin drift, and, more rarely 





* - 





i— 



Fig. 525 — Loess overlying Kansan drift, with a thin band of pebbles at the junction; 



Iowa. (Calvin.) 



the younger. It even overlies the Late Wisconsin drift in places, 

 though the Wisconsin drift-sheets are usually free from it. 1 Loess 

 does not appear in quantity between the Illinoian and Kansan for- 

 mations, nor between the Kansan and sub-Aftonian. 



Outside the drift there are often two distinct sheets of loess. They 

 are sometimes separated by a well developed soil zone, beneath which 

 the surface of the lower loess shows the effects of prolonged weathering 

 and oxidation. 2 



x Jour. of Geol., Vol. IV, pp. 929-937. 



2 Report on Crowley's Ridge, Ark. Geol. Sur., pp. 



224-235. 



