114 THE ILLINOIS GLACIAL LOBE. 



entire surface of Stephenson County, of but 1 foot, or only one-fourteenth 

 the bulk of the Silveria formation. 



In the vicinity of Rock Island several exposures of silt have been 

 found by Prof. J. A. Udden beneath the lowest deposit of till, and through 

 his kindness the writer has been conducted to them. Whether these 

 deposits are all of similar age, and whether they are earlier or later than 

 the Kansan, has not been determined. They appear to be at least as old 

 as the maximum extension of the Illinoian sheet. One of the best exposures 

 is that made by a well at the base of the Mississippi bluff, near Thirty-sixth 

 street, in Rock Island. The bluff back of the well carries about 40 feet 

 of loess and several feet of till above the level of the well mouth. The 

 exposures are not adequate to show the age of the till, though it is probably 

 Illinoian. The section of the well, which was observed while in process of 

 excavation both by Professor Udden and by the writer, is as follows: 



Section of well near Thirty -sixth street, Bock Island, Illinois. 



Feet. 



Yellow till (probably Illinoian) 5 



Black muck (Yarmouth ?) 1 



Brown till (leached 2 or 3 feet) 1 



Blue till (probably Kansan) 4 



Black calcareous silt, with gasteropod fossils 8 



Black muck 4 



Green muck with a few local pebbles 5 



Coal Measures shale. 



Total 34 



Within a mile east from this exposure, in the city of Moline, a well 

 observed by Udden reached a fossiliferous loess-like silt beneath a pebbly 

 clay at a depth of 30 feet. The well is on the Mississippi River bottom, 

 corner of Seventh avenue and Fifth street, Moline, at an altitude about 30 

 feet above the low-water mark of the river. 



A ravine on the range line between sec. 7, T. 17 N., R. 1 W., and sec. 

 12, T. 17 N., R. 2 W., exposes the following section: 



Section of ravine on range line between sec. 7, T. 17 N~., R. 1 W., and sec. 12, T. 17 N., 



R.2 W. 



Feet. 



Loess 45 



Black soil 2 



Yellowish-brown till 12 



Loess-like silt, containing fossils several feet 



Coal Measures sandstone. 



