56 The Middle Devoxian Deposits of Maryland 



Oriskany Fokmation 

 Buff or brownish rather coarse sandstone with numerous fossils. 



The fossils wero collected from the various beds of the above section. 

 The lowest division contains a profusion of individuals but a very limited 

 number of species. The succeeding bed contains a much more varied 

 fauna and contains many species diagnostic of the Onondaga. The highest 

 fauna which shows definite affinities Avith the Onondaga is in the succeed- 

 ing bed which, however, is probably a repetition of the lowest unit de- 

 scribed. The black fissile shale occurring 157 to 357 feet above the base is 

 probably to be referred to the Marcellus while the overlying bed 45 feet 

 thick contains a well defined Marcellus fauna.^ 



In this as in many other sections no very sharp line can be drawn 

 between the sediments holding the Onondaga and the Marcellus faunas, 

 the one grading into the other. Taken as a whole, however, the upper, or 

 Marcelhis, shales are decidedly blacker and comparatively freer from light- 

 colored shales than is the lower series in which green and drab-colored 

 shales predominate. 



The Tropidoleptus carinatus fauna characteristic of the Hamilton was 

 found in a bed of gray sandstone which lies not far above the base of that 

 member. 



Exposure east of Oldtown. — One mile east of Oldtown, a cut in the 

 Western Maryland Eailroad affords an excellent section of the Onondaga 

 and Marcellus shales. The Hamilton member and its fauna is also ex- 

 posed a short distance east of this cut. The section exposed here follows : 



RoMNKv Formation 

 Hamilton Member ^^^^ ^^^^,_ 



No. 13. Hard drab sandy shale: Lingula sp. undet., Spirifer 

 mucronatus, Anihocoelia umhonata. Stropheodonta perplana. Tro- 

 pidoleptus carinatus 400-|- 1060 



No. 12. Gray fine-grained sandstone, weathering to shaly beds. . 50 660 



No. 11. Drab and dark steel-gray hard shale, and covered, thick- 

 ness very uncertain, Hamilton ? (Duplication by local folding) .... 250± 610 



No. 10. Hard sandy drab shale with three or four thin bands 

 holding Aulopora sp. at east end of cut 40 360 



^ Prosser has included all the beds above the base of the black shale, 

 which occur 302 to 662 feet above the base of the section, in the Hamilton. 

 The author would place the Marcellus-Hamilton boundary about 350 feet 

 higher than the horizon selected by Prosser (662 feet above the base of the 

 section). 



