2S2 GEOLOGY OF OHIO 



This completes the review of the coal seams of the Lower Measures. 

 There is a single seam in the Lower Barren Measures that has been 

 mined in a small way for the general market. It was described in Vol- 

 ume V, under the designation of the Brush Creek coal, but a better name 

 is now proposed for it in the Pennsylvania scale, viz., the Mahoning coal. 

 Its place is about midway between the Upper Freeport coal and the Cam- 

 bridge limestone. It is in Columbiania county only that the Mahoning 

 coal has been found in volume large enough to justify its being worked 

 in systematic mining operations in Ohio, and even here the seam has 

 lost its former importance. It is here known as the Groff vein. 



No account will here be given of the several thin seams belonging to 

 the Barren Measures that are found irregularly developed within our 

 Coal Measure territority. A coal seam that reaches 18 inches in thick- 

 ness, if of good quality, is never to be despised. The time will come 

 when every such addition to our fuel supply will be carefully counted 

 and utilized. 



SECTION III. 



The Coal Seams of the Upper Productive Measures. 



Two seams, one of them of first class importance, have been 

 mapped in connection with the present volume, viz., the Pittsburgh coal 

 and the Meigs Creek coal, of our scale, which is probably the Sewickley 

 seam' of the Pennsylvania reports. Other seams also find place in the 

 Ohio series and one and another may be worked in a small way, but none 

 has importance enough to demand admission to this review. 



The Pittsburgh Coal Seam. The Pittsburgh coal is unquestionably- 

 and by all odds, the most valuable single coal seam of the great Appa- 

 lachian field. It has a far wider area, a greater average thickness, and, 

 on the whole, is of better average quality, than any other seam. At the 

 same time, it is by far the steadiest of all our seams, holding the same 

 general character from town to town, from county to county and even 

 from state to state. 



It reaches its highest development in western Pennsylvania, where 

 it furnishes a considerable portion of the gas coal of the United States, 

 and where it is also the center of our greatest coke production. This 

 highest development is attained in Westmoreland and Fayette counties- 

 As the seam is followed northward and westward from the centers named 

 it suffers some reduction in quality, even before it reaches the state line. 

 There is a distinction in all the markets which the Pittsburgh coal 

 reaches between the eastern and western mines of these Pennsylvania 

 counties, and the distinction is to the disadvantage of the latter. 



A few words will be given to a description of the character of the 

 Pittsburgh coal in this, its most characteristic field. The description is 

 drawn from the volumes of the Second Pennsylvania Survey. It is 

 everywhere a double seam, consisting of a roof coal and a main bed, 

 between which a clay parting intervenes, ranging in thickness from an 



