PENNSYLVANIAN. 439 



Feet. 



14. Redstone coal ["Pomeroy"' coal of Ohio; very persistent, 50 to 70 feet below Sewickley coal; 



30 to 80 feet above base of series in Maryland and nearly everywhere throughout basin except 

 around southwestern part of outcrop area, where not always recognized] 4 



15. Redstone limestone; apparently only in southern Pennsylvania and adjoining region of "R'est 



Virginia and Ohio, 10 to 20 feet thick, with minute "fresh- water'' ffaaeils; thins rapidly 

 southward in West Virginia and Ohio 10 



16. Pittsburg sandstone (sandstone or shale) [variable, coarse, in places pebbly, generally present 



about borders of the basin, though abruptly disappearing locally in shale and sandstone, 

 the Redstone limestone (No. 15) being apt to vanish where the sandstone is well developed; 

 in many localities lies directly on the Pittsburg coal (No. 17)] 40 



17. Pittsburgh coal [most important coal; very persistent and regular; correlated in Broad Top 



field, the Potomac basin of Maryland, through southern Pennsylvania, the northeastern 

 counties in West Virginia, and the northern portion of the basin in Ohio, but becoming 

 patchy, irregular, or absent around the southwestern part of the basin in Ohio " and West 

 Virginia, and apparently absent in a portion of the south-central interior of the deep basin; 

 yet fairly regular and workable over an area of 7,000-8,000 square miles] 12 



ANTHRACITE REGION. 



General features. — The position of tlie anthracite fields and their general relations to the 

 Appalachian folding in eastern Pennsylvania have already been indicated (pp. 430-431). The 

 Pennsylvanian synclines are relatively small, their combined area being about 650 square miles, of 

 which the area of workable coal approximates but 484 square mUes.'*^^ The anthracite fields 

 have been treated with great detail and thoroughness in an elaborate series of publications 

 for each field,* as well as in several special reports," published by the Second Geological Survey 

 of the State. The whole has been admirably condensed by A. D. W. Smith.''^^ More recently 

 the general geologic relations and stratigraphy have been briefly discussed by J. J. Steven- 

 gQjj.7B6h aj^(j ij^Q stratigraphic paleobotany of the southern anthracite field has been treated in 

 an advance publication giving correlations by the writer. '°^ 



In the anthracite region the greatest thickness of the Pennsyivanian, 2,500 feet, is in the 

 southern field; the sections cTo not reach to horizons as high in the middle fields. In the 

 northern field the deepest syncline contains 1,800 feet of Pennsylvanian strata^ 



The Pennsylvanian of the anthracite region is divided only into the Pottsville ("Serai 

 conglomerate") and the "Coal Measures." The latter are grouped according to "white ash" 

 or "red ash" coals, but these divisions are local and highly variable. The paleontologic 

 correlation of the post-PottsvUle beds is incomplete and without attempt to draw definite 

 boundaries. 



The strata in the anthracite region are in general much more arenaceous than those of the 

 bituminous series in any other part of the northern Appalachian coal field, the arenaceous 

 character being more and more predominant as the southeastern border of the region is 

 approached. Conversely, limestone seems to be unknown except in the northern field. The 

 series is moderately coal bearing, there berag as many as 25 coals, 20 of which are of workable 

 thickness, in the southern antliracite field, about 15 in the western middle field, and 16 in the 

 northern anthracite field. In the eastern end of the southern anthracite field the Mammoth 

 bed attains the remarkable thickness of 114 feet, of which 105 fecu is coal. 



PottsviUe group. — The Pottsville as a whole is most fuUy developed in the southern anthra- 

 cite field. It was somewhat arbitrarily defined by the Lesley Survey as extending from the 

 Buck Mountain coal bed, the lowest stratum of the "Coal Measures," to the top of the Mauch 

 Chunk shale (Mississippian). In the type section, the Sharp Mountain gap at Pottsville, in 

 which the "Twin" coal is regarded as equivalent to the Buck Mountain, the thickness as pub- 

 lished by the writer ^^^^ is very nearly 1,200 feet, though the Broad Mountaia section to the 



" See Bull. Geol. Survey Ohio, 4th ser.. No. 9, map; also Geol. Survey West Virginia, Rept. 2A, maps. 

 *> Atlas of the northern anthracite field, 6 pta.; eastern middle field, 3 pts.; western middle field, 3 pts.; southern 

 anthracite field, 6 pts. 



<= Repts. Progress A and AA, see also Ann. Repts. 1885, 1886, and 1887. 



