156 THE CAMBRIAN AND ORDOVICIAN DEPOSITS or MARYLAND 



miles wide just west of Williamsport. In its course through Maryland, 

 Conococheague Creek is confined to this belt of Martinsburg shale, and 

 the rugged topography caused by its erosion affords many outcrops of the 

 'strata. Exceptionally fine exposures occur, however, along the Western 

 Maryland Railway from Williamsport west to Pinesburg Station. The 

 underlying shale rock is shown almost continuously between these two 

 places. Perhaps nowhere else in the Appalachian Valley is there such a 

 continuous section of this formation exposed with all its attendant fold- 

 ing and faulting, and these railroad cuts will long remain classic ground 

 for the study of this great syncline. 



This section clearly brings out two well-marked divisions in the forma- 

 tion, the lower part consisting of a thick mass of black shale, and the 

 upper portion for the most part of yellowish-green sandy strata. These 

 two portions are distinct enough in the Massanutten syncline to be 

 mapped as separate divisions, but in the North Mountain uplift to the 

 west they grade into each other so gradually that it is impossible to map 

 them separately. 



Sufficient fossil evidence has been found in Maryland, but especially in 

 southern Pennsylvania, to show that these two lithologic divisions corre^ 

 spond to definite portions of the general time scale. The lower black 

 shale division contains, near the base, several horizons with faunas of 

 Trenton age. It is probable, although not yet established by paleon- 

 tologic evidence, that the upper part of these black shales corresponds to 

 the Utica shale of the New York section. In the area west of the Massa- 

 nutten syncline the sandy division has furnished numerous fairly well 

 preserved fossils of Eden age. In the North Mountain uplift this sandy 

 Eden division is followed by gray sandstones with a maximum thickness 

 of 450 feet in which a considerable number of Cincinnati an (Lower May?- 

 ville) fossils has been found. These gray sandstones are still included in 

 the Martinsburg shale, but the overlying soft red sandstone and red shale 

 are so distinct that they have been separated as the Juniata formation. 

 The Martinsburg shale as here developed, therefore, ranges in age from 

 the Lower Trenton to at least the Lower Maysville and comprises portions 

 of the Mohawkian and Cincinnatian series. 



