MIDDLE AND UPPER ORDOVICIAN. 



J 17-18. MARYIiAND, VIRGINIA, AND EAST TENNESSEE. 



173 



The middle and later Ordovician of the Appalachian Valley south of Penn- 

 sylvania are represented by the strata which lie between the Knox dolomite below 

 and the Clinton ("Rockwood") formation above. In many places, especially along 

 the east side of the Appalachian Valley, there is a distinct unconformity between 

 these strata and the Knox dolomite. The formations are calcareous, generally 

 limestone in the western sections but shalv or sandy in the eastern. They have 

 been described by Hayes,"""^'"' *'« CampbelV'^- ''"-''' and Keith «^*™' ^^^ as Chicka- 

 mauga limestone, Athens shale, TeUico sandstone, Sevier shale, Holston marble, and 

 Moccasin limestone; by Safford ^^^ as Lenoir limestone and Nashville or Sevier 

 shale; and by Smith ^^* as Chickamauga. Darton ^^'* applied the name Shenan- 

 doah limestone to the full thickness of limestone occurring between the Lower 

 Cambrian quartzite and the Upper Ordovician shales (Martinsburg shale), especi- 

 ally in Virginia. 



Local descriptions follow, in order from southwest to northeast. 



In central eastern Tennessee (Knoxville quadrangle) the sequence and thickness 

 of lithologic formations of the Ordovician differ somewhat in the northwestern and 

 southeastern areas. Keith ^^^^ gives the two following sections: 

 Generalized section northwest of Bays Mountain. 



Generalized section southeast of Bays Mountain. 



