Maryland Geological Survey 181 



Oeiskany Formation 



Vertical Total 



Ridgely Sandstone Memier ^^"t^n'^ilTc^^tl 



Light gray quartzitic sandstone dipping from 60° to 67° to the 

 eastward. There is considerable disturbance at the Oriskany- 

 Romney contact but the thickness cannot be less than 210 feet. 

 Spirifer arenosus (r) 210.0 277.0 



Shriver Chert Member 

 Black nodular chert with gray shale partings. Anoplotheca 

 flabellites (r), Spirifer tritulis (rr), Meristella leiitiformis ? 

 (r), Chonetes hudsonicus (r) 67.0 67.0 



II. Section at 21st Bridge 

 On the West Virginia side of the Potomac Eiver at 21st Bridge, the 

 Baltimore and Ohio Eailroad cuts across an anticline of Oriskany giving 

 an exposure from the New Scotland member of the Helderberg to the 

 very top of the Oriskany. The exposure is clean cut and complete, showing 

 the contact between the Helderberg and tlie Oriskany. Of the latter there 

 are few better exposures in Maryland. At the west side of the cut near 

 the bridge the rocks lie quite horizontal and gradually dip as one goes 

 away from the bridge until the top of the Oriskany lies at a very high 

 angle. The section as worked out by Schuehert and Rowe is as follows : 



Oriskany Formation 



Vertical Total 



Ridgely Sandstone Member *'''f'eer''thicknei 

 Heavy-bedded arenaceous limestone, gradually changing down- 

 ward into a black chert or siliceous shale. In the lowest beds 

 are found Spirifer cumberlandUr. S. concinnokleus. and Eatonia 

 sinuata. Fossils, however, are rare until 100 feet above the base 

 of this division, where the characterizing Hipparionyx fauna 

 attains greater individual and specific representation, culminat- 

 ing in the upper 100 feet 258.0 328.0 



Shriver Chert Member 

 Bedded and nodular chert and siliceous shale, with a sparse 

 fauna distinct from the Hipparionyx fauna above and from the 

 Helderbergian below. Near the base are found Anoplotheca 

 flabellites (aa), Stropheodonta arctimiiscula (r), and Ostracoda. 

 Just below the middle occur Anoplotheca flabellites (c), Spirifer 

 tribulis (c), S. paucicostatus, Beachia suessana var. immatura, 

 Anoplia nuclcata, Pholidops multilamellosa. Tentaculites aculus 

 and Diaphorostoma desmatum.. Near the top is an abundance of 

 ostracoda and some Chonetes hudsonicus 90.0 90.0 



