210 GEOLOGY OF ILLINOIS. 



The Schoonrnaker coal is locally ten and a half feet thick, and at no place in 

 the workings is it less than eight feet thick. So far as known, it is overlaid 

 directly by brown and drab alluvial clays; and, to supply the deficiency of 

 roof rock, the upper layers of the coal are left in place, the workings nowhere 

 much exceeding six feet in hight. The upper and lower benches are of clean 

 cubical coal ; while the central portion has a very irregular fracture, and pow- 

 ders readily. As a whole, the coal is impure, containing disseminated pyrite 

 and partings of calcite, and yielding a very large proportion of ash. Certain 

 portions of the bed are quite free from all these objections; but, here as else- 

 where, no pains has ever been taken to separate the good from the bad, and 

 the mine has consequently a bad reputation, though what is dug still finds a 

 ready market. The floor of this mine is composed of from four to six inches of 

 fire clay, resting upon a thin bedded, fissile, carbonaceous, micaceous sandstone, 

 which has been penetrated to the depth of four or five feet in the sump. 



This seam is evidently the equivalent and continuation of the ten-inch seam 

 of coal, accompanied by from eight to ten feet of coaly shale and shaly sand- 

 stone, which outcrops on the bluff of the Kankakee, about one and a half miles 

 northwest of the mine, in the edge of Grrundy county. Above the mine, in 

 section 8 of the same township, this seam has been worked in the bed of the 

 river, and is said to be from three to four feet thick, with a floor of a few inches 

 of fire clay resting upon the lowest beds of the Niagara limestone. The coal 

 is here, of course, greatly deteriorated by exposure ; but it is considerably used 

 by the neighboring farmers. This was the first coal known in all this region, 

 and has been worked more or less since a very early date in the settlement of 

 the country. At Schoonmaker's ford, on the county line, this seam is recog- 

 nized in a band of rotton coaly shale at the top of the bluff, and is underlaid 

 by from fifteen to twenty feet of ferruginous and micaceous shaly sandstone, 

 accompanied by concretionary nodules, which sometimes contain fragmentary 

 remains of Lcpidodendron and other plants. A short distance below the ford, 

 we find this sandstone resting upon a few feet of olive and ash-colored shales, 

 which, in turn, rest upon the shaly limestones of the Cincinnati group. Where 

 this seam has been worked in the bed of the river, four or five feet of blue clay 

 shale, with fossil ferns, have been reported as resting upon it, in some cases; 

 but, below the county line, it is overlaid only by a thin bed of purplish shaly 

 clay, entirely destitute of fossils. 



The extent of this bed is supposed to be very limited, as borings made within a 

 half mile of the shaft, on the southward and eastward, have failed to find it or 

 its equivalent, while there is reason to believe that it does not extend far north 

 of the river. The underlying shaly sandstone has been met with in small 

 patches as far north as the southwest quarter of section 21, township 34 north, 

 range 9 east, but unaccompanied by any indications of coal. Along the Des- 



