314 GEOLOGY OF ILLINOIS. 



yellow and blue clays, here and there mixed with sand and gravel. Boulders 

 of igneous and metamorphic rocks are not uncommon in it, and may fre- 

 quently be seen along the courses of the streams. Wells are not usually sunk 

 entirely through this deposit, an abundant supply of good water being com- 

 monly found before the beds of the Coal Measures are reached, though occa- 

 sionally they go deeper, and good water is sometimes obtained in the Coal 

 Measures. 



All the stratified rocks exposed in Knox county belong to the Coal Meas- 

 ures, and they comprise a series of sandstones, limestones, clays, shales and 

 seams of coal, and represent the middle and lower part of the series, from coal 

 No. 6, of the Illinois section, to coal No. 1 inclusive. 



The upper seam, No. 6, is found principally in the eastern half of the county. 

 It varies in thickness from four to six feet, and affords a good quality of coal. 

 In this and the adjoining counties, it has a clay band about a foot and a-half or 

 two feet from the bottom, and frequently several other clay partings, as the two 

 sections given below will illustrate. No. 1 was taken from a mine in section 

 15, township 10, range 4, and Nc. 2 from section 32, township 12, range 4. 



No. 1. No. 2. 



FEET. IN FEET. IN. 



1. Coal 2 10 18 



2. Clay ' ito i 



3. Coal 1 1 



4. Clay 1 "2 3 



5. Coal , 8 6 



6. Clay !1 1 



7. Coal 11 1 



No. 4 of this section is nearly always present, but is occasionally replaced 

 by clay shale, and rarely by pyrite. Partings Nos. 2 and 6 are quite variable, 

 always less than No. 4 and frequently wanting or marked by a band of shale 

 or pyrite. The principal clay parting, No. 4 of the section, is largely used as 

 a mining seam. The clay having been removed the coal above is broken down, 

 and that below taken up. 



In the western half of township 12, range 4, this coal seam has been exten- 

 sively worked. Mines have also been opened in sections 4, 5, 17, 18, 19, 29, 

 30, 31 and 32. A section of the strata on section 12, gave : 



FEET. IN. 



1. Clay shale. Not measured 



2. Limestone 1 to 3 



3. Slaty or clay shale 6 in. to 4 



4. Coal 2 " 2 8 



5. Clay, mining seam ...., 2 in. to 3 



6. Coal 1 foot 6 in. to 2 



7. Clay 2 " 4 



8. Sandstone 



