CHAPTER XIV. 



WELLS OF ILLINOIS. 



INTRODUCTION. 



In the Seventeenth Annual Report of this Survey the writer has pre- 

 sented a paper on the "Water resources of Illinois," in which the wells are 

 discussed in a general manner in connection with other water resources. The 

 data concerning artesian wells and the wells affording supplies for cities and 

 villages are tabulated in that paper, but a large number of wells which do 

 not admit of ready classification were necessarily omitted. The present 

 discussion aims to present all the reliable records collected in the State which 

 throw light upon the formations penetrated and the character of the water 

 supply. 



CLASSIFICATION OF UNDERGROUND WATERS. 



The classification of underground waters given below seems to include 

 the most important phases or classes of subterranean distribution to be found 

 in this region. It has already been presented in nearly its present form by 

 the writer in the Eighteenth Annual Report. In nearly all cases it is not 

 difficult to decide from the description to which class a given well should 

 lie referred, and it has scarcely seemed necessary, in the detailed discussion 

 which follows, to group the wells in classes. They are instead taken up by 

 counties. However, a tabulated statement has been prepared setting forth 

 the use made of the several classes of wells as sources for city water supply. 



The following are the principal classes of underground waters: 



class i. — Ground water, supplied by direct percolation of the rainfall 

 into the soil and substrata, and subject to but little lateral transmission and 

 little hydrostatic pressure. The water level rises and falls with the degree 

 of saturation by rains. 



ciass 2. — Waters in close association with streams, as in valley bottoms, 

 in which lateral transmission is great and hydrostatic pressure is small. It 



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