600 A. W. GRABAU TYPES OF SEDIMENTARY OVERLAP 



According to this reasoning, based wholly on lithic characters, the 

 Marcellus and Genesee shales of western New York should be regarded 

 as synchronous, and both should be identified with the Ehinestreet or 

 any other of the black shales of that region; for "in every [lithic] 

 feature this . . . [Marcellus] shale is practically identical with 

 many of nearly a hundred exposures . . . [of black shales of vary- 

 ing horizons] examined by the writer." 



The Chattanooga shale in the region of the Columbia quadrangle in 

 central Tennessee is described as having generally at the base a thin bed 

 consisting largely of calcium phosphate and forming the source of the 

 Tennessee black phosphate. In many cases these phosphate nodules 

 surround minute coiled shells derived from the underlying Ordovicic 

 limestones. This phosphate bed passes by gradation laterally into a bed 

 of coarse sandstone or conglomerate containing varying amounts of 

 phosphate and much water-worn material, together with some unidenti- 

 fied fish bones. Sometimes, toward the southwest, the phosphate is re- 

 placed by a fine grained gray or black sandstone, with a maximum thick- 

 ness of 12 feet in Hardin county (Hardin sandstone). Where the Chat- 

 tanooga formation rests on the Clifton or on the Fernvale formation 

 (limestones), it is always a black shale at the base. The Maury green 

 shale is generally found at the top of the Chattanooga formation. It 

 varies from a few inches to 4 or 5 feet in thickness in central Tennessee, 

 though it does not exceed 2 feet in the Columbia quadrangle. It con- 

 tains lime phosphate and Greensand grains, which are the cause of the 

 color. 



"Rarely, as in the upper part of East fork of South Harpeth creek, the green 

 shale is absent or not distinguishable, and in these cases the black shale seems 

 to pass very gradually into the overlaying green shale * which constitutes the 

 base of the full Tullahoma section."! 



The Tullahoma formation of shales passing up into cherty limestones 

 is from 200 to 500 feet thick and is believed by Ulrich to represent the 

 whole of the Waverly of Ohio ; but it is probably more correctly regarded 

 as representing only the upper part of that formation, which in southern 

 Ohio is considerably over 600 feet thick. J There is no recorded evi- 

 dence from fossils which would establish the equivalency of the Tulla- 

 homa to the whole of the Waverly, since fossils are extremely scarce in 

 the Tullahoma of Tennessee. Apparently the correlation is based on 

 position alone, as the formation succeeds the black shale, which is on a 



* The italics are the present writer's. 



t Columbia folio, p. 3. 



t Harrick : Bull. Geol. Soc. Am., vol. 2, p. 40. 



