212 GEOLOGY OF ILLINOIS. 



Lying so near the border of the basin, this seam, as well as the one previously 

 treated of, has suffered, more or less, from local displacement, besides having 

 been deposited upon a surface originally irregular. This has been the princi- 

 pal cause of its irregular^ thickness, and, to some extent, that of its variable 

 character. Where the bed lies upon a sloping floor, a large part of the impuri- 

 ties, especially the sulphid of iron (pyrite), seems to have settled away by 

 gravity and to have accumulated in the lower portions, leaving the upper part 

 comparatively pure. 



This irregularity of bottom prevents any regularity in the depth of shafts, 

 and so prevents any accurate estimate of the dip, the general direction of which 

 is toward the southwest. It also prevents any certainty as to the exact line of 

 outcrop ; since, from it, we may reasonably predicate the probable existence 

 of outlying patches, separated from the main bed by portions of barren 

 strata. Such will probably be found, when more borings shall be made beyond 

 what is now accounted the boundary of the coal area. These patches, however, 

 are likely to be small, and would not warrant any great outlay in searching for 

 them, especially while so large a portion of territory known to be underlaid by 

 coal remains undeveloped. 



So far as is yet indicated by borings, the outcrop of this is essentially as fol- 

 lows : Entering the county near the northwest corner of section 30, town 33 

 north, range 9 east, it passes diagonally to the center of the south line of this 

 section ; thence to the middle of the east line of the northeast quarter of sec- 

 tion 31, and eastward to the same point in section 33; thence diagonally to the 

 center of the north line of the northwest quarter of section 3, township 32 ; 

 thence southwest to the center of the west line of the same section, and to cen- 

 ter of south line of section 4; thence to the southwest corner of section 9, and 

 in nearly the same course to the center of section 20 ; thence due south into 

 Kankakee county. The last three or four miles of this line are determined 

 with less accuracy than the upper portion, since fewer borings have been made 

 in that part of the county. 



To the eastward of this line of outcrop, borers have often been encouraged 

 by finding beds of soft clay shale " soapstone" corresponding in general char- 

 acter with that which overlies the coal ; but, so far as T can learn, none of those 

 lower beds contain any of the nodules of carbonate of iron, often containing 

 vegetable or animal remains, which characterize ten or fifteen feet of the shale 

 immediately on top of the coal, and, in many cases at least, they probably be- 

 long to the underlying Cincinnati group, the Niagara limestone being absent 

 from this part of the county. 



The overlying shales are of very variable thickness, and are often accompa- 

 nied by bands, and occasionally by thick beds of sandstone. I am indebted to 



