June, 1907 .] 
The Devonian Limestones. 
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. 3 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.: identity 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 Company two miles 
northwest of Charleston, Indiana, along the Baltimore & Ohio 
Railroad consists of a rather soft blue marly limestone with 
some shaly layers where much weathered. This portion includes 
rather more than half of the outcrop. Above this comes a very 
fossiliferous gray limestone with much soft chalky 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, many 
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 favorably distant 
sections even in Ohio, but its cherty character, blue color, and 
3. Ibid. p. 535. 
