754 C. 0. Dunbar — Stratigraphy and Correlation 



which the Pegram limestone is supposed to be a south- 

 ward extension. 



The writer has not seen the exposure on Mills Creek 

 near Fortyeight P. O. in Wayne County, but it is 

 described by Drake (1914) as "nearly 6 feet of pebbly, 

 coarsely crystalline, gray limestone.' ' Here it rests on 

 the Brownsport group of the Silurian, while farther east 

 at Newsom it succeeds the still younger Lego limestone, 

 but on Buffalo River it succeeds the Camden chert. At 

 this locality only 45 feet of the highest part of the Cam- 

 den formation is exposed, but within a few miles west at 

 Camden it is known to be at least 164 feet thick. The 

 overlap of the Pegram limestone eastward and south- 

 eastward over the Silurian indicates that the Camden 

 chert thins out rapidly in this direction by overlap, since 

 it was closely followed by the Pegram. 



The formation is probably separated by a short inter- 

 val from the Camden chert, since the coral fauna which 

 characterizes it does not appear until about the middle 

 of the Grand Tower formation in southeastern Illinois, 

 the lower part of the latter being unrepresented in 

 Tennessee. 



? Upper Devonian Series 



f Chautauquan Group 



Chattanooga shale. — The Chattanooga shale is a wide- 

 spread formation, extending from the western valley to 

 the mountains of eastern Tennessee, and from Alabama 

 into Kentucky, overlapping many formations ranging in 

 age from Ordovician to Middle Devonian. In central 

 Tennessee it attains a considerable thickness, but in the 

 western valley it is uniformly thin and is locally absent 

 at many places, due apparently to later erosion. Here it 

 generally ranges between 2 and 10 feet, and rarely 

 exceeds 20 feet. 



The shale proper is a black, fissile, carbonaceous shale 

 of fine and even grain, and smells strongly of petroleum 

 when struck with a hammer. Crystals and concretions 

 of pyrite occur commonly and thin concretionary layers 

 of gypsum may be found near the base. 



Beneath the black shale there is usually present a thin 

 basal sandstone called the Hardin sandstone member.^ It 

 generally forms a single massive layer of fine-grained 

 muddy gray sandstone from a few inches to 3 or 4 feet 



