592 COAL MEASUKES OF MARYLAND 



horizon. The Pottsville-Allegheny boundary would thus be placed be- 

 neath the Lower Mount Savage coal and above the massive Sampson 

 Eock conglomerate. The Ellerslie coal would appear to be the Lower 

 Kittanning coal and the Upper and Lower Mount Savage coals, the 

 Clarion and Brookville coals respectively.^^ 



The discrepancy in the position of the Pottsville-Allegheny boundary 

 indicated by the flora and by the lithology is due, possibly, to the fact 

 that arenaceous beds accumulated along the steeper gradients of the 

 streams in the east, in Lower Allegheny time, while more argillaceous^ 

 sediments were forming along their lower gradients in the west. * If 

 this is the case, a line drawn between the Allegheny and Pottsville 

 formations upon the basis of lithology would rise across the strata east 

 ward and include sediments of Allegheny age in the Pottsville formation. 



The full presentation of the evidence bearing upon these points must 

 be reserved for the discussion of the floras, which will appear in a sub- 

 sequent publication.^* The thickness of the Allegheny as thus limited 

 is 250 to 300 feet. 



Pottsville formation. — The Pottsville formation consists of massive 

 sandstones, conglomerates, and interbedded shale, which, as shown by 

 David White, bear a distinctive flora. As delimited in the preceding 

 discussion, it consists in Maryland of two zones of massive sandstones 

 separated by a shale zone. Two fossil faunas are present, consisting 

 of a few brackish water species. The lower zone bears the same species- 

 southward ^^ and appears to be definitely correlated with the Quakertown 

 fauna of West Virginia. The upper zone is questionably placed at the 

 horizon of the Upper Mercer fauna of Pennsylvania.^^ The Pottsville 

 rests unconformably upon the Mauch Chunk red shale. 



Conclusion and Summary 



The preceding discussion shows that certain features of the Coal 

 Measures are persistent over large areas, the beds containing the marine 



-3 That the correlation of the individual coals of the Allegheny and Pottsville forma- 

 tions is insecure in much of the northern Appalachian coal basin is made manifest by 

 the examinaton of the accompanying plate of columnar sections of these formations. 

 Lithology and intervals are insufficient, without paleontological data, for confident cor- 

 relation. 



2* Monograph of the Carboniferous of Maryland to be published by the Maryland 

 Geological Survey. 



2^ W. Armstrong Price : Report on Barbour, Upshur, and the western portion of Ran- 

 dolph counties. W. Va. Geol. Survey. 1918, p. 786. 



-^ See chapter on Stratigraphy, where the relations of the members are further dis- 

 cussed. 



