252 GEOLOGY OF ILLINOIS. 



and a heavy limestone roof. Further south, we find its equivalent in the seam 

 worked near the Indiana Furnace, on Brouillet's creek and its branches, west 

 of Clinton, Indiana, and also at the base of the hills north of the national road 

 opposite Terre Haute. 



Immediately below this seam, and properly forming a constituent part of it, 

 though separated, near Danville, by a variable thickness of fire-clay, is the so- 

 called "Blacksmith's seam," of from ten inches to two feet of good coal. 

 Though the separation increases rapidly as we ascend Salt Fork, it is probably 

 only local, and the partings are not likely to attain anywhere the dignity of 

 distinct seams. In the Catlin shaft, the division is not noticeable, except by 

 the more ready separation of a few inches from the bottom of the main seam 

 in mining. At Georgetown, and southward, no such division is noticed. 



Both the thickness and the character of the strata between this and the 

 " Grape Creek" seam, No. 34, vary considerably. Along the Big Vermilion, 

 especially in the nighborhood of Danville, we have generally from twelve to 

 fifteen feet of fire clay, rarely with nodular limestone and soft shale, the latter 

 partly sandy, underlaid by a very compact layer of limestone, partly silicious, 

 partly nearly pure, which contains some fragmentary fossils, but nothing charac- 

 teristic. Below this, and forming the roof of the lower coal, No. 34, we have a 

 few feet of a dark drab, sometimes black shaly clay, in which no fossils were 

 noticed. Though the different beds vary as indicated in the section, the whole 

 thickness, in this part of the county, rarely exceeds twenty feet, and is often 

 not more than sixteen feet. Along Grape creek, just below the distillery on 

 the northwest corner of section 33, township 19 north, range 11 west, the 

 lower seam is covered by three or four inches of soft black shale, followed by 

 from twenty to thirty feet of drab clay shale, becoming sandy above, which, 

 two hundred yards below, are replaced by a heavy bank of sandy shales and 

 shaly sandstone, with some solid bands of quarry rock. I was unable to decide 

 from the partially covered outcrop, whether this was simply a change in the 

 character of the layers, or whether the shale had been removed, and the sand- 

 stone deposited in the eroded basin. At least forty or fifty feet of strata are 

 here exposed above No. 34, without bringing in any representative of No. 27. 

 Along the creek, above the distillery, there are indications of a low anticlinal, 

 with confused dips; and I was at one time inclined to refer to the "Grape 

 Creek" seam proper, the coal mined at and near Lafferty's, which here shows 

 characters and accompaniments intermediate between those of coals Nos. G and 

 7 ; but the weight of evidence finally turned in favor of No. 7. 



Along the Little Vermilion, below Georgetown, the intervening strata have 

 thickened up still further. It would be difficult to measure an exact section ; 

 but the following is approximately correct : 



