CORRELATION p91 



supposed, but lies nearly 100 feet ahove the Ames limestone and is hemie 

 in the position of the coal commonly called the "Elk Lick" in neighbor- 

 ing areas. The persistent limestone 100 feet above the Barton coal may 

 be correlated provisionally with the Clarksburg limestone. 



The suggested correlation of the various members of the Conemaugh 

 is indicated in the chapter on stratigraphy and will not be further con- 

 sidered here (see also plate of columnar sections). 



It is interesting to note that, associated with the thickening of the 

 strata, there is a great increase in the content of coal, so that the Cone- 

 maugh contains many coal seams in Maryland, where it is not a barren 

 formation. 



Allegheny formation. — The upper limit of the Allegheny formatio]i 

 is determined by the evidence already adduced. The lower limit, how- 

 ever, is open to question. The most important datum plane for the 

 correlation of the lower members of the Allegheny formation in the 

 typical area is the Vanport (Ferriferous) limestone. This is a thick 

 limestone, containing a profusion of marine fossils, found about 50 feet 

 below the lower Kittanning coal in western Pennsylvania. It extends 

 but a few miles east of Pittsburgh. The correlation of the lower mem- 

 bers of the Allegheny formation presents great difficulties east of the 

 latter point, owing to the absence of a trustworthy datum plane. 



An attempt has been made in the past to draw the boundary between 

 the Pottsville and Allegheny formations in Maryland by means of 

 changes in the character of the lithology. If this' criterion be employed, 

 the Pottsville-Allegheny boundary would undoubtedly be drawn above 

 the Mount Savage sandstone and probably, at some localities, above tlu; 

 Westernport sandstone. It is manifest, however, that there is a marked 

 variation in the lithology from place to place and it seems unsafe Tc 

 determine the limits of the formation over wide areas without paleon- 

 tological evidence. In view of the absence of the Yanport limestone in 

 the eastern section, an effort has been made to draw the boundary between 

 the Pottsville-Allegheny formations in Maryland by means of the fossil 

 floras. With this purpose in view, extended and detailed collections 

 of the floras have been made in Maryland and adjacent areas and also 

 in the typical sections of the Allegheny formation of western Penn- 

 sylvania. It is impossible to review the data at this point. Suffice it to 

 say that the conclusions reached by Harvey Bassler, who has been en- 

 gaged in a critical study of this problem, indicate that the profuse flora 

 associated with the Mount Savage coals are of Allegheny age, and that 

 a distinct chano-e in floras occurs a short distance beneath the latter 



