PENNSYLVANIAN. 437 



16. Brush Creek coal; Masontown coal in part; unusually persistent though generally unimportant in Broad Top 

 field, through Pennsylvania, and largely in outcrops through Ohio; "Gallitzin" coal of the eastern side; multiple in 

 division, with interbedded limestones.'^'' 



17. Mahoning limestone member; developed in eastern part of plateau field and locally associated with iron ore 

 (Johnstown iron ore). 



18. Mahoning sandstone member. Includes: (a) Upper sandstone, in places massive and conglomeratic; said to 

 be fairly persistent through much of Conemaugh exposure on east side of basin, but generally lacking on west; separated 

 from lower sandstone of the Mahoning member by highly variable shale interval with coal. (6) Mahoning coal; locally 

 present with clays in western Pennsylvania, (c) Lower sandstone; generally persistent through Conemaugh area, 

 and in places conglomeratic though locally obscure or lacking; is here and there the basal member of the formation, 

 resting directly on the Upper Freeport coal, the topmost member of the Allegheny formation. 



19. Uffington shale member; thin, local only, and crowded with marine invertebrates near Morgantown, W. Va. 

 (Contact with Upper Freeport coal.) 



The Conemaugh formation occupies, naturally, a relatively small area. It reaches a 

 thickness of over 700 feet near Monongahela River and in Maryland. Along the northerly 

 outcrop it averages not over 600 feet, and to the west and south in Ohio it falls off to 300 feet 

 or less. Coals in unusual number and thickness were developed in the Castleman basin, in 

 southern Somerset County, Pa., and in Maryland. 



Broadly viewed, the Conemaugh is an arbitrarily limited and highly variable formation, 

 largely sandstone or even conglomeratic in its lower portion, with much red and green clay 

 material and marls in its middle, and more sandstones, locally conglomeratic, in the upper 

 part, which was locally eroded before the deposition of the succeeding Monongahela formation. 



The last, so far as at present known, of the strictly marine invertebrate faunas occurs not 

 far above the Ames limestone member (No. 7 of preceding list), perhaps the most widely 

 extended of the distinctly marine members. ° According to the fossil floras, the writer is 

 inclined to draw the Westphalian-Stephanian boundary pi'ovisionally at or close above the 

 top of the Allegheny formation, the Mahoning sandstone member being interpreted as showing 

 the beginning of a more pronounced erogenic movement which seems gradually to have brought 

 about the final exclusion of the sea. On the other hand, I. C. White,°°'J citing (1) the dis- 

 covery by Dr. P. E. Raymond, in the "Pittsburg Reds" (No. 9 of list) at Pitcairn, Pa., of the 

 reptilian genera Eryops, Desmatodon, and Naosaurus, closely allied to types regarded as 

 Permian,'^" (2) a fossil obtained near the horizon of the Ames limestone member near Salt Lick 

 Bridge in Braxton County, W. Va., regarded as the tibia of a large reptile; (3) the Permian 

 aspect, according to Scudder, of the insects from about the same horizon near Steubenville,, 

 Ohio; and (4) the introduction of red sediments,* argues for the reference of all the beds above 

 the Buffalo sandstone member (No. 15) to the Permian. The evidence both of plants and of 

 mollusks is distinctly contrary to this proposed correlation. The upper boundary of the 

 Conemaugh is not yet drawn in the anthracite regions. 



Monongahela formation. — The Monongahela formation, or ' ' Upper Productive Coal Measures " 

 (XV of Rogers), is the highest of the Pennsylvanian formations in the Appalachian trough. In 

 K 17 and K 18 it occupies a small area in the bituminous regions, being for the most part confined 

 to the deeper portion of the basin ^'^^ in 'Southwestern Pennsylvania and eastern Ohio." East 

 of the Chestnut Ridge anticline in Westmoreland County, Pa., it appears only in very small 

 residual areas in the Ligonier Valley and it is represented partly also in the Broad Top and 

 Castleman basins. It is fully present in minor areas in the Potomac basin of Maryland and 

 West Virginia. 



The Monongahela as defined by I. C. White ^°^ begins with the great Pittsburg coal and 

 extends to the roof of the Waynesburg coal, comprising another somewhat arbitrarily dif- 

 ferentiated division of the Pennsylvanian. The upper part of the Waynesburg coal contains 

 Taeniopteris, Equisetites, Baiera, and Saportsea, of Permian relations, while, as stated in the 



"■ At several points local deposits of red material occur as low as the top of the lower sandstone of the Mahoning 

 member. 



6 Red beds are stated by Dr. J. J. Stevenson '^''^ to be present in the upper part of the Allegheny in northeastern 

 Kentucky. See also Phalen, W. C, Bull. U. S. Geol. Survey No. 349, 1908. 



" For areas of formations and individual coals see Geol. Survey Ohio, Repts. V and VI, Bull. No. 9, 4th ser. 



