STRUCTURE OF THE DRIFT BORDER, 47 



at its surface. It also presents the crumbling texture characteristic of the 

 Illinoian till sheet. It shows very little surface leaching, response to acid 

 beino- readily obtained at a foot or less. This absence of a marked 

 weathered zone was interpreted to be due to removal by a stream which 

 deposited the sand and silt, rather than to the time interval being too brief 

 for the development of a weathered zone. The slight inequalities in its surface 

 appear to be due to erosion. This till is referred with some confidence to 

 the Illinoian because of its physical texture and characteristics. Its thick- 

 ness, as exposed on Second street, is about 30 feet. Beneath the till there 

 are beds of fine sand and silt, in the midst of which are thin layers of clay, 

 bearing pebbles up to 2 inches or more in diameter. Similar beds in the 

 southwest part of Muscatine separate the Illinoian and Kansan till sheets, 

 as shown below. 



In the southwest part of Muscatine the altitude of the Mississippi bluff 

 is 160 to 200 feet above the river, and a remarkably full series of drift 

 deposits is, or has been, exposed. In 1894 a grading on Green street 

 afforded an excellent exposure of the upper part of the series, beginning at 

 a level about 165 feet above the river and extending down 50 feet, but this 

 is now concealed by grass. The lower part of the bluff is still exposed in 

 the large clay and sand pits west of Green street. The exposure on Green 

 street was examined by the writer when freshly graded (in 1894), and those 

 west of Green street were examined by the party of geologists in November, 

 1897. The sections are as follows: 



Section on Green street, Muscatine, Ioica. 



Feet. 



Iowan loess, partly eroded 



Brownish-black silt at base of loess - 1 i t0 " 



Pebbly black soil (Sangamon) 



Leached brown till (Illinoian) 



Brown till, unleached, many bowlders near base (Illinoian) >■-' 



Calcareous silt 



Calcareous till of brown color, probably Kansan - 



10 



Section on Mississippi bluff west of Green street, Muscatine, Iowa. 



Feet. 



Loess, perhaps not in situ - _ ° 



Till of brown color, eroded, of friable crumbling texture, characteristic of Illinoian drift.. . 15 to Jo 

 Beds of sand with even upper surface but uneven lower surface, containing a few bowlderets 



and cobblestones, but not as a rule stony 



to 12 



Gray till, with vertical cracks lined with brown material, probably Kansan 8 to20 



