328 ■GEOLOGY OF OHIO. 



maps it is not separated from the Corniferous, but is embraced under 

 the same coloring as the Corniferous. The blue stripe which is named 

 "Hamilton Group" represents in part the shale which underlies the 

 black slate, and which has been specially designated "Olentangy shale" 

 in the report on Delaware county, to which the reader is referred for a 

 statement of the subdivisions of the Ohio Corniferous, and of their sup- 

 posed equivalents in New York. The Lower Corniferous is well repre- 

 sented in the quarries in Mill Creek township. The Oriskany has not 

 been seen within the county, but it is probably conglomeratic, since it 

 has that character in Delaware county. These limestones, with the 

 Oriskany,. make up the Devonian, so far as represented within the 

 county. The rock which immediately underlies the Oriskany belongs 

 to the Upper Silurian. It is the Waterlime member of the Lower Hel- 

 derberg. The Devonian is found only in the south-eastern part of the 

 eounty, although there are some evidences, in the form of large frag- 

 ments, that it extends as far west as Marysville. It underlies the most 

 of Mill Creek and Jerome townships. The rest of the county is occupied 

 by the Waterlime. 



The Hamilton or Upper Corniferous. — This limestone occupies but a 

 small area in the south-eastern part of the county. It is hard and blue, 

 and identical with the blue stone quarried at Delaware. Any favorable 

 outcrop in that section should be thoroughly opened for building stone. 

 This part of the county, though, is mainly covered with a heavy forest, 

 and the strike of the formation is not known. Hensell £ Fox, near 

 Frankfort, have the only quarry in the county in this stone. 



The Lower Corniferous. — The Delhi stone of the Lower Corniferous is 

 quarried at a number of places in Mill Creek township. The quarry of 

 Thompson and Brown, six miles south-east of Dover, exposes about four 

 feet of fossiliferous, sometimes crinoidal limestone, in beds of two to 

 four inches. It is principally burned for quicklime, but is also sold for 

 cheap foundation stone. The lime which it makes is like that already 

 described made from the same beds at Delhi, in Delaware county. The 

 fossils seen here are Cyrtoceras undulatum, a handsome little Strophomena, 

 a large Cyathophylloid coral, the pygidium of a trilobite, and various 

 remains of fishes. There are also common a large Strophomena and a 

 small Cyathophylloid. The quarry of John Piersoll, about three miles 

 east of Watkinsville ; that of Wm. Hays, a mile north-west from Pier- 

 soll's ; those of John S. Smart, near Piersoll's, and that of Daniel Long, 

 in the north-east corner of the angle of the county, are all in the Cornif- 

 erous, and near the horizon of Thompson & Brown's. 



Oriskany Conglomerate. — The only proof that this, usually a sandy lime- 



