64 ECONOMICAL GEOLOGY. 



representative of the entire series is about ten or twelve feet of 

 Hamilton limestone, intercalated between the Niagara and the 

 lower carboniferous series. 



The next outcrop in a northerly direction is in Rock Island 

 county, where the Hamilton limestone and shale is somewhat 

 thicker, attaining a thickness above low water level of the Mis- 

 sissippi of fifty to sixty feet. On the eastern border of the 

 State no outcrop of this formation is known, but it was pene- 

 trated with the diamond drill at Tuscola in their search for 

 coal. 



In LaSalle, county the coal measures overlie unconformably 

 the Trenton limestone, both the Devonian and Upper Silurian 

 systems being absent, a phenomenon probably due to erosion 

 anterior to the carboniferous period. The geographical extent 

 of this erosion we have no data for determining at the present 

 time, but no great thickness of Devonian strata have yet been 

 revealed by the drill, either in central or northern Illinois, and, 

 as the lower gas horizon, the Trenton limestone, has failed to 

 yield it in notable quantity in any of the numerous borings 

 made through it, the writer has not been disposed to encourage 

 any considerable expenditure of capital in searching for natural 

 gas in this State. 



ARTESIAN WATER. 



Three successful attempts to obtain artesian water have been 

 made in western Illinois since the publication of Vol. VII, of 

 these reports. Two of these are in Hancock county, one at the 

 Riverside Sanitarium near Hamilton, which is located at the 

 top of the bluff of the Mississippi river nearly opposite the city 

 of Keokuk, and the other at Carthage on the prairie which 

 forms the watershed between the Mississippi and the Illinois 

 rivers. 



The Hamilton well obtains its flow from the Niagara lime- 

 stone which was reached by the drill at the depth of 680 feet. 

 The flow from this well is estimated by Dr. Ringland, the pro- 

 prietor of the Sanitarium, at 50,000 gallons per day, which I 

 feel inclined to regard as an over-estimate. The water was said 

 to rise in a rubber tube to the height of sixty-three feet above 

 the surface. 



