174 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



In northeastern Tennessee Keith **^* distinguishes the following formations: 



Generalized section of the sedimentary rocks in tJie Great Valley, GreeneviUe quadrangle. 



In southern Virginia M. R. Campbell ^^^' ^'^^ has mapped the lithologic divisions 

 named below : 



Generalized section for portion of Bristol quadrangle north of Clinch Mountain. 



The Shenandoah limestone, the comprehensive series of Cambrian and Ordovi- 

 cian limestones of the valley of Virginia, formerly known as the " Valley limestones, " 

 is briefly described by Darton,^^^ who recognized a lower division of dark magnesian 

 limestones, grading upward into lighter-colored cherty strata, and followed by purer, 

 more thickly bedded, highly fossihferous Umestone. Variations in the character of 

 these formations are noted in the reports by W. B. Rogers ®^'''' and J. L. Campbell,^^** 

 but the distinctions made have no systematic value. For central Virginia H. D. 

 Campbell "" has introduced the following classification: 



