Maryland Geological Survey 347 



STRATIGRAPHIC AND PALEONTOLOGIC CHARACTERISTICS^ 



The Jennings For:\iation 

 introductory 



At or near the base of the Jennings formation in Allegany County and 

 apparently confined to it are black, fissile shales, with a thickness of about 

 90 feet, which weather to a gray color and readily turn to soil. In Wash- 

 ington County the olive shales and thin sandstones of the succeeding 

 division rest on top of the upper Romney sandstones and the black shales 

 have disappeared by thinning out to the eastward. The black shales con- 

 tain fossils which occur in the Genesee shales of New York as for example : 

 Buchiola retrosiriata v. Buch, Pterochaenia fragilis (Hall), Styliolina 

 fissurella Hall, Bactrites aciculus (Hall), and other species. Among 

 the best exposures are those to be observed in the cut above Corriganville, 

 by the side of the National Road 23/0 miles nortlieast of Cumberland and 

 on Flintstone Creek in Gilpin. 



The black shale occurring at or near the base of the Jennings is 

 believed to represent the same horizon at the several localities at which it 

 has been noted in Allegany County. A characteristic Hamilton fauna is 

 known to extend within at least 30 feet of the black shale, and perhaps 

 to its base since the interval of 30 feet is covered, while similar recurring 

 black shales were not noted in the superjacent beds of Portage age as is 

 the case in the deposits of this stage in western New York. On account of 

 its stratigraphic position it is thought that this black shale represents the 

 reappearance of conditions in Maryland similar to those which existed 

 in central and western New York while the Genesee shale was being 

 deposited, but which were absent during that time in eastern New York 

 and eastern Pennsylvania, and it has been provisionally correlated with 

 the Genesee shale of New York. The time of its deposition may not have 

 been precisely identical with that of the Genesee shale of New York; 

 however, it is believed that the diiference in time was not great. 



The next member of the Jennings formation consists mainly of greenish 

 argillaceous and arenaceous shales alternating with thin sandstones of 

 similar color all of which weather to a yellowish-green. The sandstones 

 which usually vary in thickness from a fraction of an inch to a foot, 



^ Contributed by Charles S. Prosser. 



