180 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



Somerset Elk Lick limestone. The Harlem coal appears in many sec- 

 tions, but is distinctly absent from others. The Pittsburg reds are a 

 striking feature wherever their horizon is reached, and the Bakerstown 

 (Barton) coal bed, 75 to 80 feet below the Ames, occasionally attains 

 workable thickness. Between it and the Cambridge limestone there is 

 sandstone or sandy shale 40 feet thick, the Cowrun of Ohio. The Ander- 

 son coal is wanting and the sandstone rests on the limestone. The in- 

 terval between the Cambridge and Brush Creek limestones, ordinarily 

 about 60 feet, is sometimes filled by the Buffalo sandstone. In one of 

 the southern townships the Salzburg condition is repeated and the Buf- 

 falo is continuous with the Cowrun, giving a continuous sandstone about 

 100 feet thick. Toward the Beaver County line the Buffalo becomes less 

 conspicuous and at times is replaced in great part by shale. The sand- 

 stone sometimes cuts out the underlying Brush Creek limestone, which 

 here has all its characteristic features, and is separated by a few feet 

 of black shale from the Brush Creek coal bed, which is from 60 to 100 

 feet above the Upper Freeport. The variation in this interval is due 

 chiefly to changes in the Lower Mahoning, which at times almost dis- 

 appears. At one locality the Upper Gallitzin is at 45 feet and the Ma- 

 honing limestone at 10 to 15 feet above the Upper Freeport. 



Above the Ames there are few persistent beds. The Morgantown sand- 

 stone is constant, often forming cliffs ; a red bed 20 feet thick begins at 

 90 feet above the Ames and is present in many sections. The Pittsburg 

 limestones are irregular.* 



West from the Monongahela and south from the Ohio are western Alle- 

 gheny, Washington, and Greene, the last extending to the West Virginia 

 line at the south. The surface formation is the Monongahela and ex- 

 cept along the Monongahela river and along the northern border of the 

 area the Conemaugh is deeply buried. The exposed section at the north 

 extends but a little way below the Ames limestone. 



In western Allegheny two limestones within 30 feet below the Pitts- 

 burg coal bed are commonly found; they are more or less brecciated in 

 structure and in most localities contain minute fossils, which are sup- 

 posed to be of fresh-water types. Another at 140 to 150 feet may be at 

 the Little Clarksburg horizon. Eed shale beds were seen at 65, 89, 106, 

 175, and 194 feet, but not all of them in any one section; that seen at 

 106 is evidently the lower portion of a 50-foot bed observed elsewhere 

 at 89 feet; that at 194 feet is apparently equivalent to one seen in north- 

 ern Allegheny at 90 feet above the Ames. Within short distances the 



* I. C. White: (Q), pp. 149, 154, 158, 150, 1G0-1G5, 171-178. 



