418 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



It attains a maximum thickness of 3;000 feet in the southern anthracite fields 

 and thins away toward the north, west, and south, as shown by Barrell and Stevenson. 

 In southern Pennsylvania, Maryland, and West Virginia the lower part of the shales 

 gives way to the sandy Greenbrier limestone. Stevenson ^^^"^ sums up the strati- 

 graphic relations and nomenclature as follows : 



The Mauch Chunk is represented only by shales, or by shales and sandstones, along the 

 northerly border m Pennsylvania, but southward limestone is found with shale above -and below 

 it. This limestone, in the Allegheny Mountain region, reaches to within 30 miles of the northern 

 outcrop, while traces of it are present stUl farther north in the anthracite region. In southern 

 Pennsylvania it is double, with a siliceous division below and a more or less argillaceous division 

 above. The former is the more persistent at the north and in the central part of the basin, but 

 it is wantmg in Ohio except in the extreme southeast. Both divisions persist in Virginia, 

 Tennessee, and Alabama, as well as in the greater part of West Virginia and Kentucky. The 

 lower shales become indefinite southward and the upper shales extend as shales little beyond 

 the northern line of Tennessee. 



The whole series has been termed Mauch Chunk in Pennsylvania, and no special geographical 

 term has been applied there to any of the subdivisions except in the northwestern part of the 

 State, where Dr. I. C. White gave the name Shenango to the shale which there is the sole repre- 

 sentative of the Mauch Chunk. In Maryland the upper shales have been termed Mauch Chunk 

 and the limestone Greenbrier; in Virginia Prof. W. B. Rogers used the names Greenbrier shale 

 and limestone; the United States geologists in that State have applied the names Canaan and 

 Pennington to the shales, Greenbrier and Newman to the limestone ; Prof. Safford in Tennessee 

 divided the limestone into Mountain limestone above and the Siliceous group below, the latter 

 into the Lithostrotion and the Protean, of which the former belongs to the Mauch Chunk; to 

 Prof. Safford's divisions Mr. Hayes applies the designations Bangor and Fort Payne, with, in 

 the southeastern areas, Floyd as equivalent to the lower portion of the Bangor; in Alabama 

 the limestone is divided by Smith and McCaUey into Bangor, Hartselle, and Tuscumbia; in 

 Kentucky the divisions are Chester and St. Louis; and in Ohio Andrews termed it MaxvUle. 



Regarding the Mississippian of the Meadow Branch Mountains area of West 

 Virginia, adjacent to the Potomac,. Stose^"^ points out that these rocks are struc- 

 turally the southeasternmost occurrence of Carboniferous rocks in the northern 

 Appalachians, outside of the anthracite region. They are widely separated from 

 the main body of Mississippian sediments in western Maryland and Pennsylvania, 

 and the formations which he maps have not been positively correlated with those 

 of the broader area. These formations, .which he regards as subdivisions of the 

 Pocono group, comprise the Rockwell formation, Purslane sandstone, Hedges shale, 

 Myers shale, and Pinker ton sandstone. 



Stose describes the Rockwell formation — the basal Carboniferous deposit — ^as 

 composed of coarse arkosic sandstone, fine conglomerate, and buff shale, with some 

 dark shale containing locally thin coal beds, and gives a section of this formation as 

 seen at Sideling Hill, on the north bank of the Potomac, showing a thickness of 

 541± feet. 



The Purslane sandstone he describes as the ridge-making rock of the Meadow 

 Branch Mountains, Sideling Hill, Spring Gap Mountain, and the higher parts of 

 Town Hill, and as composed largely of heavy-bedded coarse white sandstone with 

 bands of quartz conglomerate and some soft white sandstones containing locally 

 thin coal seams. Sections of the Purslane sandstone show that the thickness varies 

 from 180 to 310 feet. 



