190 GEOLOGY OF OHIO. 



with what it is further east ; for it is not more than twenty feet in thick- 

 ness, while in central New York the Hamilton group is twelve hundred 

 feet thick. There is no mistaking the equivalence of these strata, how- 

 ever, for they are full of fossils. At Prout's Station the following species 

 are found, viz. : Spirifera mucronata, Cyrtia Hamiltonensis, Strophodonta 

 demissa, Athyris spiriferoides, Heliophyllum Halli, Phacops bufo, etc., etc., 

 the most characteristic fossils of the Hamilton. 



The Hamilton beds mentioned above are not always present; as at 

 Belville, the Huron shale may be seen resting directly upon the Cornif- 

 erons limestone, here presenting the lithological characters of the San- 

 dusky quarry stone, and containing great numbers of Strophodonta hemi- 

 spherica and other well-known Corniferous fossils. 



From the softness of the Hamilton limestone in Erie county, as well 

 as from its inconsiderable dimensions, it forms no well-marked line of 

 outcrop, but it will be often detected in sections which include the base 

 of the Huron shale and the top of the .Corniferous limestone. It may be 

 said to underlie a very narrow belt of territory, extending south-westerly 

 from the lake shore, at a point half way between Sandusky and Huron, 

 to the Lake Shore Railroad, midway between Monroeville and Bellevue. 



The section exposed at Deep Cut is as follows : 



1. Huron shale ; base. 



2. Hamilton limestone, ferruginous and cherty, with crinoids (Ancy- 



rocrinus, etc.) and corals 10 feet. 



3. Hamilton marl, with Phacops bufo, Spirifera mucronata, Cyrtia 



Hamiltonenm, Athyris spiriferoides, etc.; base not seen 20? " 



The Corniferous limestone appears on lower ground near, but the con- 

 nection is not seen. 



Over the outcrop of the Hamilton cherty limestone a lake ridge is seen, 

 with a nucleus of unworn blocks, chiefly of Hamilton limestone. The 

 railroad has here an elevation of 135 feet above the Lake ; the ridge is 

 145 to 150 feet. Broken ridges and knolls of sand, evidently one of the 

 old lake beaches, form a distinct belt in this vicinity. 



Corniferous Limestone.- — The most interesting, and perhaps the most 

 important, formation in Erie county is the Corniferous limestone. This 

 is the rock underlying Sandusky City, that which forms Marblehead, 

 Kelly's Island, Middle Island, etc. ; the source from which the greater 

 part of the lime used in northern Ohio is derived, and a rock scarcely 

 less extensively employed as a building stone than the Berea grit. The 

 upper portion of the Corniferous limestone is blue in color, and lies in 

 thin strata. It is this subdivision of the formation that is opened in the 

 quarries at Sandusky, and which furnishes the blue limestone known 



