170 IOWA ACADEMY OF SCIENCE 



the buff loess, and both above and below the sand lens, where 

 water percolation is more easy than elsewhere, the loess assumes 

 the gray color. Loess kindchen and "pipe stems'' are found 

 in the gray loess, not in the original buff type. Wherever 

 the loess is more than a very few feet thick it is buff with depth. 

 It is clear that the gray loess is not to be interpreted as a 

 distinct deposit and the same may be affirmed of the dark blue 

 masses found in the yellow loess. 



These exposures, together with numerous others between 

 Des Moines and Keokuk, seem to indicate that the gray loess 

 so common m the lower Des Moines valley may have been 

 changed from a buff original, one similar to the loess of the 

 Missouri valley except for the absence of kindchen in the Des 

 Moines yellow loess and their abundance in the Missouri valley 

 deposit. 



The pebbly fossiliferous clay, number 6 of the above section, 

 is to be considered, perhaps, as in part a result of the washing 

 by waters from the Wisconsin ice of the loess with its contained 

 fossils, and the mingling of this with clay, sand and gravel 

 from the till. No doubt it is partly the result also of the erod- 

 ing, mixing work of the ice itself. In character and general 

 appearance it is intermediate between till and loess. In places 

 it is gray, and appears as if composed of mingled gray, un- 

 oxidized Wisconsin till and gray loess. It is very common and 

 its general relations are well shown just east of 11th street along 

 the north face of the cut. Here are exposed in horizontal suc- 

 cession : drift, pebbly, yellow above and gray below, twenty- 

 five feet; grading into shell-bearing pebbly gray clay, fifteen 

 feet; replaced abruptly, but with no line of division, by loess, 

 grayish above, yellow below, thirty feet; succeeded again by 

 fossiliferous, yellow pebbly clay, twenty feet exposed. Un- 

 der all of these lies the sand lens, two to three feet thick, and 

 under this in turn is gray loess. A few feet of yellow or brown- 

 ish Wisconsin till forms the surface material along all of this 

 exposure, which is about twenty feet in height. 



To show the extreme variability in materials within short 

 distances the following section from the intersection of 12th 

 street and Court avenue is added. This is not over two hun- 

 dred feet from the second section given. Below the level of 

 12th street the following succession was shown : 



