MARYLAND GEOLOGICAL SURVEY 163 







other areas in Maryland are in the North Mountain uplift, one forming 

 the eastern slope of Powell Mountain, a second occupying Blair Valley 

 between Rickard and Sword Mountains, and the third and smallest being 

 the Punchbowl area of Bear Pond Mountain. These North Mountain areas 

 show few outcrops of rock and are generally covered by debris of the 

 sandstone formations which form the tops of the adja'cent mountains. 



FAUNAS. Although fossils must be considered as quite rare in the 

 Martinsburg shale, sufficient paleontologic evidence has been found to 

 show that faunas of Trenton, Eden, and Maysville age are represented. 

 Two zones with Trenton fossils occur near the base of the formation, the 

 Eden fauna is found in the upper sandy portion, and the topmost sand- 

 stones hold Maysville species. 



Fauna of the Basal Martinsburg Shale (Sinuites Bed of Trenton Age.) 

 The most prolific zone for fossils in the Martinsburg shale is a thin 

 band of limestone near the base of the formation which locally is crowded 

 with organic remains. This zone has been recognized at numerous places 

 in southern Pennsylvania, Maryland, and Virginia, although exposures of 

 it are less frequent in Maryland and its contained fossils here are quite 

 few in comparison with the other two states. In southern Pennsylvania 

 the 35 species described in the following pages have been found repre- 

 sented by fairly good specimens, while an additional dozen or more forms 

 are known from poorly preserved fragments. A still larger fauna occurs 

 in this bed at Strasburg, Virginia, where excellent exposures for collect- 

 ing occurred in the past. 



The most striking and common fossil of this zone is the gastropod 

 Sinuites cancellatus which has given rise to the name of the Sinuites bed. 

 In the Chambersburg-Mercersburg folio of the U. S. Geological Survey, 

 this zone has been considered as a transition bed between the Black River 

 and Trenton and placed at the top of the Chambersburg limestone. As 

 indicated later by Ulrich in his Revision of the Paleozoic Systems, the 

 early Trenton aspect of its fauna is more marked than that of the Black 

 River, and the reference of the bed to the basal Martinsburg is believed to 



