244 GEOLOGY OF OHIO. 
that forms the base of the Devonian. It is distinctly divisible, on pale- 
ontological and lithological differences, into two parts, the upper part em- 
bracing the “blue limestone,” which shows some relations to the Hamil- 
ton, and the lower part embracing the lighter-colored and dolomitic 
limestones of the Upper Helderberg of the Mississippi basin. They are 
both well represented and favorably exposed in the western part of 
Crawford county. The former is about thirty-five feet thick, and is ex- 
tensively wrought at Delaware and Sandusky. The latter is quarried at 
Marblehead, on the peninsula north of Sandusky, and at Columbus, in 
Franklin county, and is about seventy-five feet thick.** 
In Crawford county the exposures of the limestones are mostly con- 
fined to the Broken Sword Creek. Beginning in section 18, Holmes 
township, the Upper Corniferous appears first on the land of S. F. Saw- 
yer, where it has been worked a little. It makes a floor-like bed to the 
creek, rising but few inches above the water along the banks. Beds are 
three to five inches thick, containing Strophomena rhomboidalis, Wahlenb., 
and numerous crinoidal stems. Mr. C. K. Stephens’s quarry is on the 
next “eighty,” toward the south. About four feet of hard, blue lime- 
stone can here be made out, although much of the quarry is subject to 
inundation by the creek, showing a decided dip to the north-east. The 
stone is in beds of about four inches, varying below that thickness, 
making a good flagstone. Some of it is harsh on weathering, although 
plainly argillaceous and sometimes with vermicular or fucoidal mark- 
ings. It is also liable to be shaly, or slaty, irregularly. Lenticular 
flakes cleave off. It has distinct purely calcareous bands of sedimenta- 
tion. It contains Cyrtia Hamiltonensis and a species of Tentaculates. It 
also holds casts of large coiled cephalopods. Its general facies is that of 
a firm limestone, nearly free from magnesia, but containing irony, bitu- 
minous, and argillaceous impurities. The next quarry in descending the 
stream is that of Christian Reiff, in beds of the Upper Corniferous, stone 
undistinguishable from the foregoing. The quarry of Mr. Perry Wilson 
is opposite that of Nicholas Poole, on the S E. 4 section 24. The stone 
here is the same essentially as that at Stephens’s,’but is undoubtedly in 
a lower horizon, exposed six or eight feet. The Bucyrus corporation 
owns a quarry here in the same beds of the Upper Corniferous. 
The Upper Corniferous also occurs on Mr. Edward Cooper’s land, N. W.4 
section 33, in Liberty township. It is but little opened and cannot be 
seen in situ, although there is no doubt of its being so. The pieces that 
have been taken out are thin and fossiliferous, Spirifer mucronatus being 
* See Geology of Delaware County. 
