76 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



Medina formations are to be found in position, but not in any thick- 

 ness, and the Clinton and Medina i-epresented genei'ally by Professor 

 SafTord's beds of transition. They appear to be chiefly the thin 

 feather edges oi* beveled wedge sha[)ed ends and abut against the 

 underlying Nashville series of rocks. That this is the case is seen by 

 the fact tliat these beds increase in tlaickness as they go westwai'ds, 

 until they reach their heaviest development in the valley of the 

 Tennessee River. The Lower Helderberg formation is also well 

 developed in the Tennessee River valley, but thins out before it 

 reaches the side of the basin, as none, or at least very doubtful, traces 

 of it have been found in the western escarpment. 



A general section of the e;i stern escarpment or margin of the basin 

 from the gorge of the Cumberland on the north east to the valley of 

 the Elk River in the south, and extending along the whole eastern 

 side gives in descending oi'der. 



Lower Carboniferous. 



Siliceous, of which cherty limestones calcareo-siliceous rocks and 

 heavy layers of solid chert are quite characteristic. 



Tlie Siliceous group includes two divisions — 



b. The Lithostrotion or "Coral bed consisting of cherty limestone, 

 fossiliferovis, often criiioidal, sometimes siliceous and argilla- 

 ceous, and everywhere characterised by the Coral Lithostrotion 

 Canadense. This bed is equivalent to tlie St. Louis limestone. 



(I. The lower or Protean bed, a series of strata, silico-calcareous 

 in the main often limestone, often sky-blue silico-calcareous and 

 sometimes argillaceous rock weathering into shale ; the series 

 containing as a characteristic feature heavy layers of chert 

 ranging in thickness from one inch to two feet, alternating 

 with the other rocks of the member. It often holds layers 

 and locally heavy beds of crinoidal Limestones. The esti- 

 mated thickness of the Siliceous group in Tennessee is from 300 

 to 500 feet. 



With the exception of a small ])atch in Short Mountains in 

 Cannon County the Lithostrotion beds do not appear in the 

 escarpment upon any of the sides of the basin. 



