254 GEOLOGY OF ILLINOIS. 



Geology. 



The geological formations appearing at the surface in this county 

 comprise the Quaternary, including the loess and drift 5 the lower por- 

 tion of the Coal Measures, including the three lowest seams of coal; 

 and the St. Louis and Keoknk divisions of the Lower Carboniferous 

 limestones. 



The entire area of the county, except the valleys of the streams, is 

 covered with beds of Quaternary age, ranging from thirty to a hun- 

 dred feet or more, in thickness, and presenting the same general fea- 

 tures that have been given as characteristic of this formation in the 

 reports on the adjoining counties. Good natural exposures of these 

 beds are but rarely found here, and the observer is compelled to rely 

 mainly on such information as can be obtained from the well diggers, 

 or others engaged in surface excavations, as to their thickness and gen- 

 eral character. In the railroad cut on the north bank of Crooked creek, 

 just below Colinar, .the following section of Quaternary beds was seen : 



Soil 1 to 2 feet. 



Ash colored, marly clay (loess) 8 to 10 ' ' 



Reddish-brown clay 5 ' 



Sand and gravel, partially stratified 15 to 20 " 



This exposure is considerably below the general level of the prairie, 

 and the beds seem to have been subjected to some sifting process since 

 its original deposition, giving to it the general characteristics of " modi- 

 fied drift." In the shafts of Colchester the drift clays generally range 

 from thirty-five to forty feet in thickness, and consist of buff or brown 

 clays, with gravel and boulders, passing downward at some points into 

 blue clays, or " hard pan." Boulders of metamorphic rocks, of various 

 kinds, and of all sizes up to a diameter of two or three feet, are scat- 

 tered in considerable numbers in all the gulches and streams that cut 

 through the drift beds, and are most abundant in the lower part of the 

 drift deposits. No indication of the presence of an ancient soil, under- 

 neath either the loess or the drift, was seen at any of the points visited 

 in this county; nor did we learn that it had been observed by any one 

 else. The wells are seldom sunk to the bottom of the drift, and hence 

 afford no indications of what may underlie the boulder clays in this 

 county. 



At Bushnell a boring for coal passed through 112 feet of these Qua- 

 ternary deposits before reaching the bed rock, in the following order : 



No. 1. Soil 2 fc(lt 



No. 2. Yellow clay ..12 " 



No. 3. Sand o " 



No. 4. Blue boulder clay . . 61 ' ' 



No. 5. Bine and yellow sand ... 35 " 



112 



