STRATIGRAPHY OF FOSSILIFEROUS MEMBERS 131 



Elk Township, where it consists of very patchy, shaly limestone and 

 flint. 



Faunally the Black Flint member resembles the Lower Mercer 

 limestone, although it is much less fossiliferous both in number of 

 individuals and in species; gastropods are likewise very rare. Bryozoans, 

 mostly Fenestellidae, are the most abundant class of fossils represented, 

 and are more numerous individually than in any other member of the 

 Pottsville formation of this State. The greater part are, however, not 

 sufficiently well preserved to make satisfactory identification possible. 



Conditions of Deposition 



The black flint and shaly limestone were deposited during the 

 closing shallow water stage of Pottsville time, and mark a continuation 

 of the same conditions which had existed during the deposition of the 

 McArthur limestone. During the entire interval which elapsed be- 

 tween the formation of the Tionesta and Brookville coals, shallow 

 waters favorable for the deposition of limestone prevailed over the 

 region; sediments, however, were carried to the sea and deposited at 

 varying rates, resulting in the formation of calcareous shales and sand- 

 stones, and shaly limestones. While the Black Flint member was 

 deposited, the sea supported fairly abundant life, whose remains are 

 excellently preserved in the shaly limestones. The formation of the 

 flint on the horizon was similar to that of the Upper Mercer member. 

 At the close of the shallow water period, swamp conditions again pre- 

 vailed during which the basal member of the Allegheny formation, the 

 Brookville coal, was laid down. 



Description of Geologic Sections and Collecting Localities 



Jackson County. One of the best exposures of Black Flint is 

 located in Washington Township in the road just north of the Town 

 House in Section 22, and it is also found capping the hill to the west., 

 The calcareous, shaly limestone outcrops on top of the hill about one- 

 fourth of a mile south of the above locality where blocks of limestone 

 are scattered over the field to the east of the road. The deposit is 

 extremely fossiliferous and affords excellent collecting. The geologic 

 section measured from the old Glen Nell mine in the western part of 

 Section 21, to the hill capped with Black Flint west of the Town House 

 shows the entire thickness of the Pottsville formation, as well as the 

 relation of the Black Flint to the underlying members (Locality 87) z 1 



'Stout, W., Geol. Surv. Ohio, Fourth Ser., Bull. 20, p. 183, 1916. 



