PROGRESSIVE OVERLAP 607 



sandy beds are fossiliferous, containing fenestella?, linguae, and brachio- 

 pods. The age of these shales in this section has not been determined. 

 They are, however, classed as Devonic, together with the Black shale, 

 though from what is known of these deposits farther northeast their age 

 is, at least in part, lower Mississippian. The thickness of the formation 

 is 1,100 feet. It is succeeded by the Newman limestone, which includes 

 100 feet of massive blue limestone at the base, followed by 500 feet or 

 more of gray calcareous shale and shaly limestone. The basal portion 

 is highly fossiliferous, containing crinoids, corals, and brachiopods. It is 

 succeeded by the Lee conglomerate (Pottsville). Northwest of Chil- 

 howee, some 30 to 35 miles, in the Walden ridge, the Newman limestone, 

 700 feet thick, rests directly on the Chattanooga shale, which is here 80 

 feet thick and rests disconformably on the Eockwood. The Newman is 

 here mainly a marine limestone, with chert nodules in the base. Its age 

 is Saint Louis and it is succeeded by the Lee conglomerate. Northeast- 

 ward, in the Clinch mountains of northeast Tennessee and southwest 

 Virginia, the Grainger shale and Black shale are both well developed.* 

 At Big Stone Gap, Virginia, the Black shale, which is at least 500 feet 

 thick, rests on sandstones of late Helderbergian age.f The Black shale 

 contains an abundance of Lingula ligea and Schizobolus concentricus, 

 both late Devonic species. The age of the base of the shale in this place 

 is therefore Upper Devonic. Professor Williams studied the section at 

 Big Stone Gap in great detail, and he found "that the following arena- 

 ceous shales and sandstones began as very thin intercalated sheets, thin 

 as paper at first, far down in what, to the casual observer, appeared to be 

 pure black shale." t 



Farther eastward, at Big Moccasin Gap, Virginia, the following section 

 was made by Williams and Kindle :§ 



Feet 



7. Limestone and shale (Mississippian) 



6. Soft yellowish clay and crumbling sandstone 100 



5. Hard, drab colored sandy shale and sandstone 40 



4. Conglomerate bed near top of 3 feet. . } 



3. Hard, bluish gray to drab sandy shale ^ 



2. Black shale, varying to gray, and much crushed and folded 150 



1. Tough quartzitic fine grained sandstone 75 



"In the Estillville folio, 2 is called the Chattanooga Black shale, and 3 to 6 

 are assigned to the Grainger shale. The lowest fauna obtained from the sec- 

 tion is from the lower part of 3, about 20 feet above the Black shale." 



* Estelville folio. 



t Williams and Kindle : Bull. U. S. Geological Survey, no. 244, p. 28. 



t Williams : Southern Devonian formations. Am. Jour. Sci., vol. iii, 1897, p. 389. 



§ Williams and Kindle : Loc. cit, p. 30. 



