Maryland Geological Survey 417 



included in tlie Chemung on the geological map of Washington County, 

 because of the ease of drawing the base of the Chemung at the top of the 

 upper Parkhead conglomerate, elsewhere they have been included in the 

 Parkhead member. 



The thickness of this division varies from 300 to 400 feet. 



Woodmont-Parkhead Boundary. — The boundary between the Wood- 

 mont and Parkhead members is usually rather distinct, though at places 

 it is very difficult to determine its exact position. Massive sandstones 

 usually develop at the base of the Parkhead, which are conglomeratic in 

 the eastern sections, although thick sandstones may also occur in some 

 places in the upper part of the Woodmont member. The lower sandstones 

 of the Parkhead can be distinguished at many localities by being bluish- 

 black when freshly exposed. Upon weathering they become butf-colored 

 and break into large, irregularly shaped pieces, in contrast with the 

 Woodmont sandstones which usually break into flat platy pieces, due to 

 the presence of clay. The shale of the Parkhead is, as a whole, more 

 arenaceous and tends to break more irregularly than the Woodmont shale. 

 At many places in Washington County a bright red band forms the top 

 of the Woodmont member. The distinctive feature, however, is the 

 occurrence of a great profusion of fossils in the basal sandstones of the 

 Parkhead, among the most abundant species being Camarotoechia congre- 

 gaia var. parklieadensis, Tropidoleptus carinatus, Spirifer {Delthyris) 

 mesacostalis and, in the western sections, Spirifer marcyi var. superstes. 

 At places these fossils are so abundant as to render the rock almost a 

 coquina. 



The lowest fossiliferous beds of the Parkhead are usually found on the 

 slope of the ridge facing the subjacent strata. 



Chemung Sandstone Member 



Character and Thickness. — The Chemung sandstone member over- 

 lies the Parkhead member with which it is so intimately connected by 

 transitional beds as to render their discrimination diffjcult. It consists of 

 alternating shale sandstone and conglomerates, the percentage of sand- 

 stone generally increasing toward the top of the formation. The shale 

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