Devonian Era in the Ohio Basin. — Clay pole. 19 
Though these beds lie approximately on the margin of the 
Silurian and Devonian domains, they cannot be regarded as 
a dividing horizon, inasmuch as they occur through several 
hundred feet of strata, part of which lies in one system and part 
in the other. But on Big Darby creek, near Georgesville, a 
series of red and white clays is found, which apparently lies 
just on the parting plane, and which, if not of secondary 
origin, may be taken as locally, at least, forming a Siluro-De- 
vonian frontier line. 
Besides the main outcrop another and a shorter one occurs 
on the western side of the Cincinnati arch, extending from 
the lake to the Indiana state-line. Along this line, however, 
the surface is so deeply covered with drift deposits that the 
underlying strata can be seen only in a few places. 
Thickness and Section. — The whole thickness usually as- 
signed to the Corniferous limestone in Ohio is about seventy- 
five feet, but nowhere does the whole of this appear contin- 
uously. The most nearly complete section which has been 
described is that shown in the northeastern part of Franklin 
county, along the Scioto river, near Dublin. The following 
account is condensed from the Geology of Ohio.* 
"At the base of the section, on a level with the water and probably 
about ten feet above the top of the Corniferous limestone, is a bed of 
cutting stone about ten feet thick, and over this lie five feet of thinner 
beds four or five inches thick, two of which hold flint concretions with 
such fossils as Murchisonia, Loxonema, and Pleurotomaria. Then fol- 
low nineteen feet of thin white limestones, crowded with fossils, which 
furnish good building stone and a strong white lime. These are the 
Delhi beds (in part) of Prof. N. H. Winchell. Eleven feet of shaly 
limestone follow, the upper Delhi beds of the same author, having little 
economic value and capped by a very thin but remarkable four-inch 
layer called the "Bone-bed," composed more or less, and often in great 
part, of the fossil teeth and other parts of fishes, chiefly of the genus 
Onychodus, whose sigmoid teeth are not infrequently found in the 
mass of fragments. This stratum extends through the formation 
wherever shown in Franklin county, but only in a limited area does it 
present all its points of interest. Elsewhere scarcely a square foot can 
be found which does not contain some fragment of a tooth or plate, 
but here these remains make up the substance of the bed." 
The strata beneath the Bone-bed constitute what was called 
by Dr. Newberry the Columbus limestone, f They form the 
• Vol. iii. pp. 605-611. 
Geology of Ohio, vol. i, p. 143. 
