REVIEW OF GEOLOGICAL STBUCTUEE. 11 



have called the Columbus limestone, a bluish gray and thin-bedded stratum 

 above, opened in the quarries at Sandusky and Delaware, and designated 

 in Volume I of this report, the Sandusky limestone. Professor N. H. 

 Winchell, who made the surveys of a number of counties in the central 

 and northwestern portions of the State, in his reports on Delaware and 

 Paulding counties (Geol., Vol. II, pp. 272, 335), proposes to place the 

 Sandusky limestone in the Hamilton Group, and divide the Corniferous 

 into two members, which he identifies with the Onondaga and Corniferous 

 limestones of New York. There seems, however, to be no sjood ground 

 for this classification. The distinction between the Onondaga and Cor- 

 niferous limestones of New York is not marked nor constant there, and 

 the whole formation is now generally regarded by geologists as one, and 

 to this the term Corniferous is applied. It is quite certain that no evi- 

 dence has yet been obtained which can be relied upon for identifying the 

 Onondaga limestone in Ohio. 



In regard to the position of the Sandusky limestone, it must be said 

 that the weight of evidence is in favor of retaining it in the Corniferous. 

 It is true that the Hamilton period is but a continuation of the Cornif- 

 erous ; the Hamilton strata being deposited in the same basin, and from 

 the same sea, but at a time when this had become somewhat shallowed, 

 and its sediments were more earthy and carbonaceous. There is even 

 in New York much in common between the fossils of the two groups, and 

 all the fossils which Professor Winchell relies upon as criteria for distin- 

 guishing the Hamilton from the Corniferous, are found in both ; hence, 

 their presence in the Sandusky limestone is no proof of its Hamilton 

 age. It should also be said that quite a number of fossils are found in 

 the Sandusky limestone which are regarded as characteristic of the 

 Corniferous, such as : Spirifera acuminata, S. gregaria, StropTwdonta hemis- 

 pherica, Pentamerus aratus, Tentaculites scalaris, as well as the fishes, 

 Onychodus sigmoides, Macropetalichthys Suilivanti, Rhynchodus secans, Machse- 

 racanthus major, etc. 



THE HAMILTON GROUP. 



As originally defined by the New York geologists, the Hamilton group 

 of New York consisted chiefly of blue calcareous shales traversed by a 

 . thin band of impure limestone — the Encrinal limestone — and capped by 

 another, the last of the calcareous sediments of the Devonian sea, called 

 the TuUy limestone. This group rests on a black shale — the Marcellus — 

 and is overlain by a similar carbonaceous deposit, to which the name 

 Genesee slate was given. These strata are highly fossiliferous, containing 

 many species which are peculiar to the group, with also a considerable 



