WELLS OF IROQUOIS COUNTY, ILLINOIS. 655 



only by McLean and Lasalle counties. Watseka, the county seat, is sit- 

 uated a few miles east of the geographic center. The Iroquois River enters 

 the county from Indiana in the northeast part, and after passing westward 

 to Watseka it turns northward and enters the Kankakee a short distance 

 north of the county line. This stream, with its tributaries, drains almost 

 the entire county. It is a widely-branching drainage system, yet the num- 

 ber of drainage lines is too few to afford escape for the surplus rainfall, and 

 there are extensive marshes within its drainage basin. 



The county is mostly occupied by a basin whose borders lie not far 

 beyond the county limits. On the west and south this basin is limited by 

 the prominent Bloomington morainic system; on the north the basin is 

 limited by the Marseilles moraine, which follows nearly the line of Iroquois 

 and Kankakee counties; on the east it finds a natural limit in the Iroquois 

 moraine, which traverses the eastern portion of the county. This basin is 

 due entirely to drift aggregation, for the underlying rock apparently stands 

 higher in the low part of the basin in the northern portion of the county 

 than in the rim of the basin on the west and south. 



This basin is found to be a favorable locality for obtaining- flowing- 

 wells from the drift, and several hundred have already been made, which 

 have been discussed by the writer in the Seventeenth Annual Report of this 

 Survey. There is a perceptible increase of head in passing from north to 

 south. There is an increase also in passing from near Watseka either east- 

 ward or westward. There is little doubt, therefore, that the absorbing 

 areas are found on the east, south, and west borders of the basin. This is 

 contrary to the interpretation made by the residents, who quite generally 

 suppose the supply to be derived from the Kankakee marsh on the north- 

 east, a marsh whose altitude is in the main below the level of the lower 

 parts of this basin. 



The drift is largely a soft till to a depth of 75 or 100 feet, though in 

 the northeastern part of the county there is a surface sand a few feet in 

 depth capping the till and which connects with the sand of Kankakee 

 County mentioned above. The till is found to be underlain at many points 

 by a black soil and by beds of peat and shell marl. With the peat and 

 marl there is usually considerable sand, which is a source for the flowing 

 wells. After these beds of peat and sand are penetrated a harder till is 

 entered than the surface sheet. In some cases this till is found to include 



