STRUCTURE OF THE DRIFT BORDER. 55 



The well at Dr. Sloat's penetrates the following beds: 



Section in well of Dr. William Sloat, in Denmark, Iowa. 



Feet. 

 .. 6 

 .. 20 



Yellow silt or loess (Iowan) 



Brownish-yellow clay, slightly pebbly (Illiuoian ) - - - - - 



Mucky clay, largely of gray color and containing a few small pebbles (Yarmouth, and possibly 



Kansan) " ' 



Brownish-yellow till (Kansan) '" 



Dark-blue till, with beds of sand yielding water _ J> 



Total depth 



The well at Mr. Conaro's was carefully observed by the writer during 

 its excavation, and has the following section : 



Section in well of James Conaro, in Denmark, Iowa. 



g 



Yellow silt or loess (Iowan) V.""1'",'tW-"'"\ in 



Brown clay, not calcareous, with occasional pebbles, 3 inches or less m diameter (Illmoian ) 10 



Soil and grayish subsoil, slightly pebbly, not calcareous (Yarmouth) 5 



Brownish-yellow till, leached for 6 feet at top, remainder very calcareous (Kansan) j^> 



49 

 Total depth 



At Mr. Blackinton's well, which was also personally observed during 

 its excavation, the upper 20 feet is a thoroughly leached clay; the remainder 

 is calcareous till of brownish-yellow color, which includes thin beds or 

 pockets of sand and extends to the rock, which is struck at a depth of 54 

 feet. In this connection it may be remarked that several of the wells in 

 the vicinity of Denmark penetrate yellow till below the Illinoian drift sheet 

 to a depth of 25 or 30 feet, there being little or no blue till above the rock. 

 At the public well, however, a blue-black till occurs at 52 to 63 feet. Expo- 

 sures on ravines both north and south of the village also have a dark blue- 

 black till beneath the yellow at a level 15 or 20 feet below the top of the 

 Kansan sheet of drift. Possibly this is pre-Kansan till. 



On the bluff north of Fort Madison a well made at the residence of 

 Mrs. Heitz reached a depth of 315 feet without entering rock. Blue till was 

 entered at 27 feet, which, with the exception of a thin sand bed, presents a 

 solid mass 260 feet in thickness. Beneath this till, in the lower 26 feet of 

 the well, there is a cemented gravel. Exposures in neighboring ravines 

 indicate that the Illinoian drift sheet on the bluffs at Fort Madison is not 

 more than 20 feet in depth. The thick bed of blue till passed through 

 in the well is apparently as old as the Kansan, and includes perhaps an 

 earlier drift sheet. Along the Mississippi bluff above Fort Madison there 



