June, 1907.] The Devonian Limestone?. 185 



portion of the formation in central Ohio includes a fossil coral 

 reef which is frequently very pronounced. 



The corresponding formation in southern Indiana is the 

 Jeffersonville limestone which agrees so closely in appearance 

 with the upper portion of the Columbus limestone that specimens 

 taken from the Speed quarries near Sellersburg Indiana could 

 not be distinguished from samples taken from the quarries at 

 Marble Cliff. This identity is not merely lithological but 

 extends also to the fossil content. The abundant species of the 

 two limestones are the same and even some of the zones known 

 here in Ohio [Spirifer acuminatus (Conrad), Spirifer gregarius 

 Clapp, coral, etc.] can readily be located. The coral zone or 

 fossil coral reef at Jeffersonville is on a far grander scale than the 

 similar zone known in the Columbus limestone but it seems to 

 occupy the same horizon or so nearly the same as to suggest that 

 they may have been contemporaneous and probably formed 

 portions of a great barrier reef of the Devonian Sea along the 

 shores of the Cincinnati island. 



At the Falls of the Ohio the Geneva limestone has thinned 

 out so that the Jeffersonville becomes the lowest formation of 

 the Devonian and rests directly upon the Louisville limestones 

 (Niagara) of the Upper Silurian.'' Some writers have included 

 the Geneva with the Jeffersonville limestone on the same ground 

 that the lower portion of the Columbus limestone is retained 

 with the upper in the same formation, viz.: identitv of fossil 

 content. 



The greatest deviation from a nearly perfect identity is to 

 be found between the Sellersburg beds and the Delaware lime- 

 stone, and yet even here there is that element of similarity which 

 is so evident in the lower deposits. The Sellersburg beds as 

 seen in the quarry of the Standard Cement Companv two miles 

 northwest of Charleston, Indiana, along the Baltimore & Ohio 

 Railroad consists of a rather soft blue marlv limestone with 

 some shaly layers where much weathered. This portion includes 

 rather more than half of the outcrop. Above this comes a verv 

 fossiliferous gray limestone with much soft chalkv white chert 

 giving it a mottled appearance. And finally above this comes 

 about two feet of very cherty fossiliferous limestone. Where this 

 formation is not covered by the New Albany black shale the 

 upper part has weathered into a red mud leaving its fossils, manv 

 of which are silicified, in a free condition and well preserved. 



The Delaware limestone which, from its similarity of fossils 

 and stratigraphic position, corresponds in a general way to this 

 Indiana formation, is too variable to compare favorablv distant 

 sections even in Ohio, but its cherty character, blue color, and 



3. Ibid. p. 535. 



