52 THE ILLINOIS GLACIAL LOBE. 



Along the ridge in southeastern Henry County, as in northwestern 

 Des Moines County, wells not infrequently pass through a bed of muck or 

 peat at the base of the Illinoian drift sheet. In a well made by Andrew 

 Johnson, li miles south of New London, there were logs and wood, occu- 

 pying a space of nearly 4 feet, found at a depth of 40 to 45 feet from the 

 surface. The writer obtained specimens of the wood and of peaty material 

 associated with it, which await specific identification. Mr. Johnson reports 

 the section of the well to be as follows : 



Section in well of Andrew Johnson, 1§ miles south of New London, Iowa. 



Feet. 



Yellow clay, without pebbles (loess) 6 



Pebbly yellow clay (Illinoian) 20 



Sand 3 



Blue pebbly clay (Illinoian) 12 



Peat and wood (Yarmouth) 4 



Gray gummy clay, with lew pebbles (Yarmouth) 10 



Total 55 



A well made by J. M. Lee, 3 miles northeast of New London, passed 

 through a bed of black muck containing wood, just before entering rock, at 

 a depth of 105 to 110 feet. This probably underlies the Kansan sheet of 

 drift. 



The drift of Lee County, as of counties to the north, belongs mainly to 

 the sheet which underlies the Illinoian. Numerous exposures, and also 

 well sections, show the Illinoian drift to have a thickness of but 20 to 30 

 feet on the plain east of the terminal ridge, and 30 to 70 feet on the ridge. 

 The average thickness of the combined drift sheets in the county is prob- 

 ably at least 100 feet. On the borders of the Mississippi the thickness 

 exceeds 300 feet, as shown by a well on the bluff north of Fort Madison 

 and another at Mont Clare. The deposit of loess coating the Illinoian drift 

 in this county has an average depth of only about 6 feet. Between the loess 

 and the Illinoian drift there is a well-defined soil (Sangamon), usually of 

 black color. At the top of the Illinoian drift there is often a mucky clay 

 containing only fine pebbles, but the greater part is a stony till with 

 occasional bowlders and numerous rock fragments 1 to 6 inches in diameter. 

 As noted above, this sheet of drift is often so thoroughly leached from top to 

 bottom that no response with acid can be obtained. Whether this feature 

 is notably characteristic of the drift border for some distance to the north 

 and south has not been determined. 



