DEVONIAN. 275 



350 feet thick, the whole the equivalent of the New York Oriskany and the same 

 as "the Monterey sandstone of the Piedmont folio." 



The Ronaney shale is described by Prosser as consisting of thin black shales, 

 sharply distinguished from the Oriskany,- followed by drab and bluish argillaceous 

 to arenaceous shales and thin sandstones, the whole 1,600 to 1,650 feet thick, and as 

 representing the Marcellus and Hamilton of New York. Kindle ^°^ has since differ- 

 entiated the Onondaga in Maryland at the base of the Romney. 



Of the Jennings formation, the lower part is composed of thin black argUla- 

 iceous shales, regarded by Prosser as the equivalent of the Genesee shale of New 

 York; followed by olive to bluish argillaceous shales, regarded by Prosser as repre- 

 senting the Naples of the Portage of New York, and green arenaceous shales, 

 containing a Chemung fauna; the toial thickness is 3,800 to 4,000 feet. 



The Hampshire formation is described by Prosser as consisting of alternating 

 red, flaggy, and massive sandstones and arenaceous or argillaceous shales, 2,000 

 feet thick, equivalent to part of the Catskill of New York. 



An important description of the Lower Devonian and Silurian of " Maryland 

 is given by Schuchert,^" who lists the species of each horizon and correlates the 

 strata with the New York section. 



I-J 16. TENNESSEE, KENTUCKY, AND NORTHWESTERN ALABAMA. 



The Devonian formations of Ohio and Indiana thin toward the south where 

 they lap unconformably upon the low land surface of Silurian limestones. Kindle *^'^ 

 states : 



The Devonian formations below the New Albany shale are frequently entirely absent in 

 the Kentucky sections, and where present they are usually represented by only a few feet of 

 strata. The Sellersburg beds have not been seen south of Louisville. The attenuated character 

 of the lower Devonian beds in Kentucky has been generally explained as due to thinning out. 

 Prof. N. S. Shaler did not recognize any stratigraphic break at the base of the New Albany shale 

 and regarded it as the equivalent of the New York Devonian formations down to the Oriskany, 

 where the Corniferous was wanting in the Kentucky section. The writer has found sections which 

 show unconformity between the New Albany shale and the beds below in Kentucky. This 

 interval of erosion which has been detected at the base of the Black shale explains the entire 

 absence of the Devonian limestone at many localities and its extreme thinness where present. 



According to Schuchert ""^ and Foerste '"" the Devonian formations in western 

 Tennessee represent, where present, Helderberg, Oriskany, Onondaga, and later 

 Devonian time, the highest strata being the black Chattanooga shale. The distri- 

 bution of these strata is very irregular. In many places they are absent and locally 

 they are represented only by beds from 1 foot to a few feet in thickness. Their normal 

 sequence is as follows: Linden formation (basal Helderbergian age), Camden chert 

 (lower Oriskany age), limestone of Onondaga age, and Chattanooga shale, with 

 phosphatic beds at its base and Hardin sandstone member and shales above. 



The following notes on the Linden are abstracted from the article by Foerste : 



The Linden at Perryville, Term., immediately succeeds the Brownsport (Silurian). It con- 

 sists of "fairly solid crinoidal rock," 10 J feet, at the base, with ■ comparatively few fossils 

 (Orihofhetes worthanus, RhipidomeUa oUata, and Striatopora issa) ; softer, partly crinoidal, partly 

 fine-grained rock more or less interbedded with clay, 11^ feet, richly fossiliferous (StropJieodonta 



