16 GEOLOGY OF ILLINOIS. 



beds, and is, perhaps, as complete a section of the Coal Measure deposits as 



could be made at any locality in the county : 



FT. IN. 



Brown shale 6 



Hard, gray, concretionary limestone 4 to 6 



Covered slope, with partial outcrops of shale 50 



Brown, sandy 'shale 15 



Coal 



Clay shale and iron ore 2 6 



Coal 2 2 



Fire clay .' 2 to 3 



Clay shale, passing downward into bituminous shale. 12 



Sandstone and sandy shale " 20 to 25 



St Louis limestone, to river level 30 



i 

 The main coal seam at this point, ranges from twenty-four to thirty inches 



in thickness, and affords a coal of fair quality, though as the work had been 

 suspended for some time when we last visited the locality, the opportunity for 

 examining the coal was not as good as could be desired. It seemed to be 

 rather free from pyrites, and the analysis, which will be found on a subsequent 

 page, shows its quality to be fully equal to the average of western bituminous 

 coals. It is overlaid by about thirty inches of clay shale, the upper part of 

 which is quite ferruginous, and forms an impure iron ore about a foot in thick- 

 ness. Above this, there is another thin seam of coal, which was four inches 

 thick at the only point where we found it exposed. These coals are overlaid 

 by a thick bed of brown shale, which was only partly exposed, but appeared to 

 be about sixty-five feet in thickness, above which was a bed of hard, gray, con- 

 cretionary limestone, from four to six feet or more in thickness, and above this 

 we saw a few feet of brown shale, which was the highest bed of the Coal Meas- 

 ure series met with in the county. The concretionary limestone contained a 

 number of species of Coal Measure fossils, among which we collected, Spirifer 

 lineatus, Athysis subtilita, Terebratula lovidens, Productus semiretkulatus, Fusu- 

 lina, sp? andjoints of crinoidea, and small turbinated corals. 



Below the main coal seam there are two or three feet of fire clay, which 

 passes downward into a black shale, which is said to have been reached at the 

 depth of fourteen feet below the coal, but was not penetrated. This black 

 shale probably represents another coal seam, which may be developed at some 

 point in the county thick enough to be worked. Between this and the St. 

 Louis limestone, we found a partial outcrop of sandy shale and sandstone about 

 twenty-five feet in thickness, which forms the base of the Coal Measure de- 

 posits in this county. The Coal Measures, as developed here, seem to include 

 the horizon of at least three coal seams, the lowest being represented by the 

 black shale ; but so far as could be learned from the few openings made in at- 

 tempting to mine coal in this county, only one seam has yet been found of 



