WELLS OF ILLINOIS. 557 



RELATION OF THE DRIFT TO ORDINARY WELLS. 



The general relation of the drift to the ordinary wells of Illinois and 

 western Indiana is set forth in PI. XXIV. It will be observed that with the 

 exception of a few counties in the northern and southern ends of Illinois 

 the wells are largely obtained from the drift, This relation is shown in 

 detail in the discussion which follows. 



GAS WELLS. 



Wells Avhich yield an inflammable gas are found in many counties of 

 the State, instances of which are presented in connection with the water 

 wells. This gas in some cases appears to be derived from the decay of 

 vegetal matter contained in the drift, either in the form of peat and muck 

 beds or as timber scattered through the drift. It is probable, however, that 

 the underlying rocks are an important if not the chief contributor, in which 

 case the pressure of the gas within the drift is due to the resistance which 

 compact drift beds offer to the escape of the gas. Not only the shales but 

 certain limestones in this region have been found to contain gas. But it 

 does not seem to have accumulated in such great quantities as in the gas 

 fields of the neighboring States of Indiana and Ohio. It rarely reaches a 

 pressure of 20 pounds per square inch. 



TABULATION OF SOURCES FOR CITY WATER SUPPLY. 



The following table embraces all the cities and villages in Illinois hav- 

 ing water works whose source of supply has been ascertained. It is based, 

 in part, upon data collected by the writer, and in part upon data found in 

 the Manual of American Water Works for 1897. 1 Through the aid of this 

 publication the statistics have been properly rounded out and brought down 

 to date. In towns with the letter "M" appended the Manual of Water 

 Works is the authority. The wells are classified according to the scheme 

 above outlined (pp. 550-551). Many details concerning the city water- 

 supplies appear in the subsequent discussion by counties. 



' The Manual of American Water Works, 1897, edited by M. H. Baker, Engineering News Pub. Co., 

 New York. Contains the history and descriptions of the source and mode of supply, pumps, reser- 

 voirs, standpipes, distribution systems, pressures, consumption, revenue and expeuses, cost, debt, and 

 sinking fund, etc., of the water works of the United StateB and Canada. 



