244 GEOLOGY OF OHIO. 



that forms the base of the Devonian. It is distinctly divisible, on palse- 

 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 HamUtonensis and a species of Tentaculites. 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. \ 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. \ 

 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. 



