ERIE COUNTY. 193 



Of Macropetalichthys the only portion yet found is the cranium. This 

 is composed of a number of geometrical plates of which the external 

 surface is beautifully tubercled. It is known to most of the quarrymen, 

 and by them it is generally regarded as the carapace of a turtle. It is, 

 however, in fact, the cranium of a large fish, as any one will plainly see 

 if they will take the trouble to compare with it the cranium of our 

 common sturgeon. No teeth have been found connected with the cranio 

 bones of Macropetalichthys, though many heads apparently complete have 

 been discovered. I have, therefore, been led to conclude that, like the 

 sturgeon, this fish was toothless. 



Onychodus was an equally large fish, of which the cranial bones were 

 much more numerous and easily separated, so that they are generally 

 found detached and scattered through the rock. The jaws of this fish 

 are not unfrequently met with. They are a foot or more in length, and 

 are studded with teeth along the upper margin. The most singular fea- 

 ture in the structure of this fish is formed by a crest of seven large, 

 curved, pointed teeth, which, attached to an arch of bone, were inserted 

 between the extremities of the under jaw, apparently acting like the 

 prow of a ram. These teeth are quite abundant in the Sandusky lime- 

 stone, the smaller and more curved ones somewhat resembling the claw 

 of some of the cat tribe, a resemblance which suggested the name I have 

 given to the genus — claw-tooth. 



Oriskany Sandstone.- — Beneath the Corniferous limestone, on the Penin- 

 sula, and near Castalia, a thin band of sandstone is visible. This holds 

 the position of the Oriskany sandstone in New York, and though it has 

 here yielded no Oriskany fossils, they are said to have been obtained 

 from it in Indiana ; and there is little doubt, therefore, that it should be 

 regarded as the equivalent of the Oriskany sandstone. 



Waterlime. — The upper portion of the Silurian system is, in Ohio, rep- 

 resented by the Waterlime and Salina formations. Of these, the Water- 

 lime is the uppermost and by far the most conspicuous. It underlies a 

 larger portion of Ohio than any other formation except the Coal Meas- 

 ures. It composes all of Catawba Island, Put-in-Bay, and the other 

 islands of that group. Erie county just reaches the edge of the Water- 

 lime area, and, as has been mentioned, it is in this rock that the subter- 

 ranean channel is excavated through which flows the stream of water 

 that forms Castalia Spring. 



'Bhe Waterlime group is probably about one hundred feet in thickness.. 

 The upper portion is a nearly pure dolomite, the lower an argillaceous 

 limestone, some of which is well adapted to the manufacture of hydraulic 

 lime. 



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