168 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



along the roads crossing the mountains, and here the fauna is known only 

 from sandstone debris along their lower slopes. In southern Pennsyl- 

 vania, on the contrary, good exposures of the fossiliferous strata are found 

 along several turnpikes crossing the mountains. The best fossils have 

 been procured from such outcrops along Jordan Knob, one and a half 

 miles northeast of Fort Loudon, Tuscarora Mountain, two and a half 

 miles southeast of McConnellsburg, and Cowans Gap, five miles northeast 

 of McConnellsburg. Two fossiliferous zones are known in the Eden 

 portion of the Martinsburg shale, one at the top of this portion and the 

 second 400 feet lower. The faunas, listed on next page, show that there 

 is little difference between these two zones. 



Fossils of the Maysville Sandstone Division, Martinsburg Shale. As 

 explained on a previous page the unfossiliferous red sandstones and shales 

 immediately overlying the Martinsburg shale have been distinguished 

 and mapped in southern Pennsylvania as the Juniata formation. Upon 

 stratigraphic grounds these red beds are undoubtedly the equivalent of 

 the Lower or Red Medina (Queenston) shales of New York. Litho- 

 logically the rocks are similar and in each area they are underlaid by 

 strata with Cincinnatian (Maysville) fossils and followed by the White 

 Medina (Tuscarora) sandstone. The sandstone underlying the Juniata 

 formation and following the sandy shales of Eden age, although covering 

 the well-defined Middle Cincinnatian (Maysville) division of geological 

 time have not hitherto been separated from the Martinsburg shales in 

 Pennsylvania and Maryland. As their area of occurrence in Maryland is 

 so small and good outcrops are almost wanting, the practice of uniting 

 these strata with the Martinsburg shale is continued in this volume. 



Exposures along the turnpike crossing Tuscarora Mountain, one and 

 one-half miles southeast of McConnellsburg, Pennsylvania, have afforded 

 fairly well-preserved specimens of the species listed below. All of these 

 fossils occur at the top of the lower division of these sandstones in a bed 

 characterized by Orthorhynchula linneyi. This Orthorhynchula bed 

 everywhere marks the dividing line between the Lower Maysville (Fair- 



