Stevenson.] 



286 



[Dec. 18, 



remain rare in our coal fields until the workings become more extensive 

 and in closer vicinity than now. At present, it is possible only to show 

 the marked changes in the intervals between our coal beds. In doing 

 this, I shall draw all illustrations from the northern portion of the Great 

 Bituminous Trough, which includes Western Pennsylvania. 



Lower Goal Group. — The total thickness of this group is subject to 

 great variations. In Pennsylvania it is from 270 to 650 feet ; in West 

 Virginia from 200 at the Pennsylvania line to nearly 700 in Randolph 

 County, and nearly 900 on the Great Kanawha, in Ohio from to 

 In each case the Mahoning Sandstone has been omitted. For detailed 

 examination, I choose the two coals known as the Upper Freeport and 

 Kittanning, in Pennsylvania, and as Nos. VI and IV in Ohio. 



Along Yellow Creek, in Ohio, the varying interval between these two 

 coals is finely shown in a continuous exposure from the Ohio River to 

 Irondale, a distance of seven miles. The coals are known locally as the 

 "Big" and "Strip" veins, and between them occurs No. V, locally 

 known as the "Roger." I give only four sections for comparison : 



These show a variation from 80' to 160' within five miles ; the most 

 marked change being in the interval between V and VI. 



In Guernsey and Muskingum Counties, Ohio, a much more interesting 

 series of changes occur along Wills Creek and the Muskingum River. 

 This line of section is an important one, as the coals can be traced almost 

 without break. Coal IV is accompanied by its Gray (fossiliferous) 

 Limestone, and VI is everywhere seen in the hills. Beginning on Wills 

 Creek, in Guernsey County, about seven miles north from the Central 

 Ohio Railroad, we find near the Salt Works, the two beds 8 feet apart. 

 Somewhat more than a mile further down the Creek, IV is mined 

 by shaft and is 28 feet below VI. Near Liberty, the interval is 40' ; at 

 Bridgeville, 105 feet. Still following the Creek and crossing into Mus- 

 kingum County, we find the interval at Johnson's Mills, 40 feet ; at 

 Frew's Mills, 90 feet; at the Salt Works near the Muskingum River 

 about the same ; near Dresden, about 100 feet, and further down the 

 river 110 feet. The line of least interval seems to run northwestwardly 

 through Guernsey County, from the starting point to a little east from 

 Johnson's Mills, the beds diverging on each side of this line. The struc- 

 ture in a cross section is somewhat as appears in this figure, the upper 

 line representing VI, and the lower IV. 



At some distance further, northeastward, a similar relation exists 

 between the coals. Across the intervening space VI can be traced quite 



