STRATIGRAPHY 571 



Monoiigaliela formation. 

 Conemaugh formation. 

 Allegheny formation. 

 Pottsville formation. 

 Unconformity. 



POTTSVILLE FORMATION 



Character and ihickness. — The Pottsville formation of Maryland con- 

 sists of massive sandstones and conglomerates interbedded with shales 

 and lenticular beds of coal. The lower beds are locally absent, owini*; 

 to the pronounced unconformity that limits it below. The entire forma- 

 tion thickens southwestward by the successive appearance of lower and 

 lower beds in that direction. 



The upper limit of the Pottsville is questionable. If the lithologicii.l 

 character of the sediments be the determining factor, then the Mount 

 Savage sandstone, and perhaps also the Westernport sandstone, should 

 be referred to the Pottsville formation, since they resemble the sedi- 

 ments of the latter formation. If the fossil flora be the determining- 

 criterion, then, according to the work of Harvey Bassler, the base of the 

 Allegheny formation must be drawn beneath the lower Mount Savage 

 coal, as has been done in this work. 



As thus defined, the thickness of the Pottsville formation in Maryland 

 varies from 100 to 250 feet. 



Members. — It comprises the following members in descending order: 



Homewood sandstone— Sampson Rock sandstone. Thick and mas- 

 sive sandstone, locally conglomeratic. Well exposed at Samp- 

 son Rock west of Frostburg. 



Upper Mercer shale and fauna. 



Upper Mercer coal — local. 



Lower Mercer coal— local. 



Upper Connoquenessiug sandstone. 



Quakertown shale and fauna. 



Quakertown coal. 



Lower Connoquenessiug sandstone. 



Sharon coal — local. 

 Unconformity. 



Underlying formation — Mauch Chunk red shale. 



Faunas. — A conspicuous feature of the section is the occurrence of 

 two brackish water faunas, which have been termed the Upper Mercer 

 and Quakertown faunas in the preceding table. The Upper Mercer fauna 

 is meager and has been observed at but few localities. The Quakertown 

 fauna is more persistent and has been recognized toward the southwest 



