442 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



between the northern anthracite region and the regions to the south have already been men- 

 tioned. Between the southern and middle fields numerous correlations have been made by 

 the State survey of the anthracite regions, as shown on the mine maps and in the "Summary 

 final report." Others affecting in particular the northern field have been proposed by Steven- 

 sonj'^'* who inclines to the belief that the post-Pottsville beds also thin to the north and that 

 the deep part of the northern anthracite field in the WUkes-Barre and Nanticoke region may 

 contain beds younger than the topmost in the southern anthracite field. Of this there is, 

 however, Httle proof. The inclusion of the Mammoth coal bed in the Allegheny formation has 

 been indicated by the writer,'^" who is disposed to place the Allegheny-Conemaugh fine as high 

 as the Holmes coal bed in the southern areas, or as the Baltimore or Checker coal bed in the 

 northern anthracite field. Harmonious with this is Stevenson's conclusion ''^"^ that the marine 

 fossils of the Mill Creek limestone of the Second Pennsylvania Survey reports, 688 feet above 

 the Baltimore coal bed, are as old as Conemaugh and may be older. These fossils, as reported 

 by Heilprin*^^ and Girty,^"^ comprise a distinctly marine invertebrate fauna, with Chonetes, 

 Eumicrotis, etc. Three other thin limestones occur in the interval covering 320 feet below the 

 hmestone to which the name MiU Creek was apphed by the Second Pennsylvania Survey, and a 

 black shale with a marine fauna hes about 250 feet above that hmestone. The occurrence 

 of these marine hmestones in the northern anthracite field is especially interesting, as is also the 

 apparent absence, so far as yet reported, of typical marine faunas from any horizon in' the 

 southern field. The Oliphant coal bed, the supposed equivalent of the Hillman coal bed, would 

 seem from the paleobotanic evidence to be older than the Monongahela formation. 



In the southern anthracite field the higher coals have furnished plants regarded by the 

 writer as of Monongahela age, but no beds of Permian age have yet been recognized in the 

 anthracite regions. 



CENTRAL APPALACHIAN REGION. 



General features. -T— To the south, in the next section of the Appalachian trough, the Penn- 

 sylvanian strip in J 17 and the southeast corner of J 16 becomes narrow gradually in West 

 Virginia and rapidly in eastern Kentucky. We have here only the southward continuation of 

 the great plateau (bituminous) field, which merges into the Cumberland Plateau. Except for 

 the Frostburg-Potomac and Cheat Mountain basins, which are isolated along the eastern margin 

 of the coal field, the separating anticlines being eroded, the eastern margin of the Peimsylvanian 

 is fairly parallel to the general direction of the Appalachian folding. For portions of its extent 

 the boundary is an overthrust fault, as, for example, St. Paul, Va., where the Cambrian is'thrust 

 on the Pottsville. Other important overthrusts which have caused the exposure of older beds 

 in the interior of the field are those along Pine Mountain, in eastern Kentucky and Tennessee, 

 and the Sequatchie Valley, in eastern Tennessee. Aside from the folds mentioned above or 

 in the previous section the Pennsylvanian of J 17 and J 16 is relatively horizontal. 



The higher formations of the Pennsylvanian continue southward from K 17 and K 18 in 

 greatly reduced area and markedly changed character, though the general sequence of the 

 members is essentially the same. The principal changes pertain to composition of the beds as 

 well as to thickness. 



MonongaJiela formation. — The Monongahela territory practically falls within a scalene 

 triangle whose southeast and west sides roughly conform to lines drawn from Cumberland, 

 Md., and Cambridge, Ohio, to Big Sandy River in Lawrence County, Ky. In Maryland the 

 formation measures 240 to 270 feet;"^ it is considerably thinner on its western outcrop in 

 Ohio and it reaches its greatest thickness — 400 feet — in north-central West Virginia. It is 

 thin in the deeper portion of the broad syncline, farthest from the old shore lines. It is notable 

 that the limestones, which form so large a part of the formation in southwestern Pennsylvania, 

 disappear soon after entering West Virginia, being replaced by red and green shales and sand- 

 stones. The Sewickley coal enters farther into the basin than the Pittsburg, but the Uniontown 

 is the only one which appears to traverse the entire deeper part of the basin. ''°^* 



