THE CARBONIFEROUS SYSTEM. 157 



several places ; is a little over two feet in thickness — a very pure, semi- 

 cannel coal, but, like all the coals of the barren group, it is unreliable. 

 This, is found directly beneath the crinoidal limestone, and is numbered 

 coal 76 by Prof. Stevenson. Coal No. la, in the same region, is 65 to 90 

 feet below the last mentioned, and is usually but a few inches in thickness. 



In Jefferson county two seams of cannel coal are found high up in the 

 Barren Measures, but they are of poor quality, and are local. 



In Muskingum and Guernsey counties the Barren Measures contain 

 more coal and limestone than farther north and east ; but none of the 

 coals have any considerable value or constancy. The thickness of the 

 group is here from 300 to 350 feet, or about 100 feet thinner than on the 

 Ohio at Steubenville. In this estimate I include only the strata between 

 the Sheridan and Pomeroy coals — i. e., between No. 7 and No. 8. This 

 interval in southern and central Ohio can hardly be called the Barren 

 Measures; but it contains no seams of coal which in permanence and 

 dimensions compare with those above and below. Prof. Andrews re- 

 ports a limestone which traverses the Barren Measures in eentral and 

 southern Ohio at a distance of about 225 feet below the Pomeroy coal. 

 This he calls the "Cambridge" limestone. It is not distinctly recog- 

 nizable in the counties lying north of the National Koad. 



THE UPPER COAL MEASURES. 



In Ohio, as in Pennsylvania, the interest in the Upper Coal Measures 

 centers mainly in the Pittsburgh seam, as this is by far the most impor- 

 tant both as regards thickness and persistence. By the Pennsylvania 

 geologists it has been denominated Coal No. 8, or H, according as num- 

 bers or letters were used to designate the seams in ascending order. As 

 has been already learned from the preceding pages, the Pittsburgh coal 

 forms No. 8 of the Ohio series, being the first workable seam of the 

 upper group. Above this we have on the Ohio three workable coals, 

 with three or four smaller ones distributed through three hundred feet 

 of strata, which have the same general character with those that com- 

 pose the Lower Coal Measures — i. e., they are alternations of fire-clay, 

 coal, shale, limestone, and sandstone. In the interior of the State the 

 Upper Coal Measures form a group of equal or greater thickness, but 

 they contain a smaller number of workable coal seams. That which has 

 been called by Prof. Andrews the "Cumberland" seam is almost the only 

 one that deserves to be classed with the strongly marked and wide-spread 

 seams which compose the lower group. There are also comparatively 

 few deposits of iron ore in the Upper Coal Measures, and none of the fire- 

 clays are, so far as yet known, equal to those under Coals No. 3, No. 5 and 



