700 THE ILLINOIS GLACIAL LOBE. 



A well near the waterworks in the Vermilion Valley penetrated to 

 supposed Upper Silurian limestone, which it enters at a depth of 1,075 

 feet. The thickness of drift at the Danville Junction well much exceeds 

 that of other wells in the neighborhood, and indicates that a preglacial 

 valley was entered by the boring. 



At Fithian, in the western part of the county, wells are usually obtained 

 from sand or gravel- associated with the till at depths of 50 feet or less, but 

 oik- well was found to have a depth of 90 feet, of which the lower 15 feet 

 is in rock. 



At Fairmount rock is entered at slight depth, and wells usually are 

 obtained at less than 50 feet. 



At Indianola wells are obtained from sand or gravel below till at a 

 depth of about 30 feet, a strong supply of water being found at this depth. 



At the village of Ridge Farm the wells are usually obtained at a depth 

 of 20 feet or less, in sand associated with till. 



The flowing wells near Potomac, in the north part of the county, 

 referred to above, usually penetrate the following series of drift beds, the 

 section being furnished by Greorge Piatt, a well driller who has sunk sev- 

 eral of the wells : 



Generalized, section offlotoing wells near Potomac, Illinois. 



Feet. 



Yellow pebbly clay (Wisconsin) 10- 12 



Blue clay, soft like putty, and containing few pebbles (Wisconsin) 60- 70 



Hard, stony clay, or ferruginous crust 1- 3 



Sand and gravel, with artesian water 6- 10 



Hard, partially cemented, sandy clay 25- 30 



Sand and gravel, with artesian water 5 



Hard, partially cemented, sandy clay 15- 20 



Sand and gravel, with artesian water several feet 



Very few records of deep wells were obtained in this county outside 

 the villages just discussed. The record of a farm well, made in sec. 31, 

 T. 23, Pi. 13 W., shows 240 feet of drift, rnainly till of a blue color, at the 

 bottom of which water was obtained in sand and gravel. A well in sec. 36, 

 in tin- same township, penetrated drift a depth of 160 feet without reaching 

 rock, and a well near Alvin a depth of 173 feet. 



