662 



CHARLES S. PROSSER 



CONCLUSIONS 

 The fauna found in the railroad cut at Pinesburg is composed 

 of species which are of common occurrence in the Trenton lime- 

 stone of New York,, and the lithological appearance of the rock 

 is that of typical thin-bedded exposures of that limestone. There 

 seems no question but that the upper part of the Shenandoah 



Fig. 4. — Shenandoah limestone in the Pinesburg quarry west of Pinesburg, Md. 



limestone is correctly correlated with the Trenton limestone. 

 The lower part of the Shenandoah limestone contains Cambrian 

 fossils ; but the line of division between the Cambrian and Lower 

 Silurian, which apparently is not indicated by any physical 

 break, has not yet been determined in the Great Valley. It is 

 hoped that future work in Maryland or West Virginia may give 

 us more definite information concerning the composition and 

 limits of this great limestone formation. The bluish to black 

 calcareous and very argillaceous shales which succeed the Shen- 

 andoah limestone and form the lower part of the Martinsburg 



