LOESS AND THE IOWAN DRIFT. 361 



drift in this part of the territory, and is not only itself divided 

 into two more or less distinct divisions, but is separated from 

 the Kansan drift either by a layer of Buchanan gravel, includ- 

 ing a ferretto zone, or by gumbo, or by both gumbo and the 

 gravel. Where the loess rests directly upon the ferretto, as in 

 the lower part of an exposure on the north side of the road in 

 the southwest quarter of section 1 r, T. 79 N., R. 7 W., the line 

 is quite sharp. Where gumbo and the gravel separate the 

 loess from the drift, as in the middle slope of the same section, 

 the line between the gumbo and the loess is less distinct, the 

 intergradation occurring chiefly within one to three inches of 

 thickness. The same is true of cases in which gumbo directly 

 separates the loess from the drift, as in the first exposure east 

 of the foregoing section, where there is but one loess, passing 

 within three to six inches into a gumbo-like layer containing 

 a few small pebbles and coarse grains of sand, chiefly in its 

 lower part. In none of the exposures examined in that part 

 of the county were fossils found below what is clearly loess. 



The three remaining sections, mentioned on p. 464, 1. c, as 

 containing fossil shells mingled with pebbles, are here con- 

 sidered separately: 



The section on Sixth street, west of Harrison, in Davenport, 

 is still much as McGee found it. The only fossils found in 

 the loess of this section are Succijiea avara. The writer 

 found none of these below the line between the loess and the 

 underlying drift, but McGee reports that they "extend to 

 and just within the pebbly horizon." This might be true 

 without proving the identity of the two deposits. Succinea 

 avara, judging from its present occasional occurrence upon 

 exposed rocky slopes, might have lived among plant-tussocks 

 when some of these pebbles still projected above the old sur- 

 face, and when the whole was buried under loess dust the 

 shells and pebbles were apparently mingled in a very narrow 

 horizon near the line of division. 



The writer was not able to find the exposure described as 

 being on the Princeton road near the middle of section 20, 



