158 THE CAMBRIAN AND ORDOVICIAN DEPOSITS OF MARYLAND 



Although the above section applies in general to all of the Martinsburg 

 shale areas in Maryland and adjoining states, a conspicuous exception to 

 the development of tha Eden division is to be noted in the Massanutten 

 syncline area. Here the lower part is the usual thick mass of black 

 carbonaceous shale with the Sinuites bed at the base and the Corynoides 

 bed higher, but the upper portion consists of yellowish-green speckled 

 sandstone so easily recognized that it has been mapped as a separate 

 member. On fresh exposure this rock is found to be a greenish-gray 

 arkose of feldspar and sand with the speckled appearance due to the 

 weathering of the feldspar into kaolin. Small streams draining into 

 Conococheague Creek have cut very rugged picturesque ravines in these 

 strata. 



The black carbonaceous shale becomes quite calcareous at the base and 

 appears to grade into the underlying Chambersburg limestone. How- 

 ever, a distinct line of unconformity separates the two formations as 

 evidenced ^by the varying age of the topmost bed of the Chambersburg 

 in different parts of the valley. Fossils are sometimes abundant in these 

 basal calcareous beds of the shale and the frequent occurrence of the 

 gastropod Sinuites gives its name to the bed. A fauna of almost 50 

 species has been recognized in the Sinuites bed of Pennsylvania and 

 Virginia, but in Maryland the bed, although recognized, has yielded 

 few fossils. 



Thirty or more feet above the base of the shale a second f aunal zone is 

 encountered. Here the small comma-shaped graptolite Corynoides is so 

 abundant that it forms a convenient designation for the bed. This Cory- 

 noides bed has been recognized in several places in Maryland particularly 

 at Williamsport and at Pinesburg Station 'on the east and west sides 

 respectively of the Massanutten syncline. This fauna is small in num- 

 bers, but it constitutes an interesting horizon throughout this part of the 

 Appalachians. 



Following the Corynoides bed are the typical black carbonaceous and 

 dark gray unfossiliferous shales of the lower Martinsburg which are so 

 readily recognized on surface outcrops by the " shoe peg " fragments left 



