Maryland Geological Survey 49 



purit}'. They play a less important role in the Maryland sections than 

 in Pennsylvania, the dark and drab shale almost, if not entirely, supplant- 

 ing them locally. 



The thickness of this member varies from 100 to I.jO feet. 



Fauna. — The Onondaga member contains numerous species many of 

 which are found in the Marcellus and Hamilton of New York. Associated 

 with them, however, are some which are restricted to the Onondaga of New 

 York, including Anoplotheca acutipiicata , which is probably the most com- 

 mon member of the fauna, and several trilobites. 



Eomney-Oriskany Boundary. — Unconformable relations between the 

 shale of the Onondaga member and the Oriskany sandstone are strongly 

 suggested by the extremely abrupt and complete change in the character 

 of the sediments at the top of the Oriskany sandstone. The lithologic 

 change is from a coarse sand to a very fine-textured shale. The faunal 

 change is equally abrupt. The unconformity which appears to exist be- 

 tween the Oriskany and the Onondaga shale member is to be correlated 

 with the well-known one at the base of the limestone of Onondaga age in 

 western New York, Indiana, and Kentucky. Bowe has shown that a 

 conglomerate develops locally at the base of the Eomney as in the section 

 at Warren Point, Pennsylvania, affording additional evidence of this 

 unconformity. Again, the thickness of the Oriskany decreases from 417 

 feet at Tonoloway to 52 feet at Warren Point, but 15 miles northeast of the 

 former place suggesting erosion of the Oriskany. 



Marcellus Black Shale Member 



Character and Thickness. — The IMarcellus member of the Romney 

 formation in Allegany County is composed principallv of fissile black 

 shale some of which weathers to a yellowish or buff color on long exposure. 

 In comparatively fresh exposures, however, as in the railroad cuts at 21st 

 Bridge the shales are either black or rusty brown after some weathering. 

 The black shales are shown to best advantage in these cuts although, on 

 the Williams Road, 3^/0 miles southeast of Cumberland, is, perhaps, the 

 most nearly complete exposure of this division with an approximate thick- 

 ness of 500 feet. l7i the lower part of some exposures are bands or nodules 

 4 



