Prossek — Hamilton and Chemung Series. 



95 



( Catskill formati< >n. 



Portage formation. 



f Genesee slate 



Marcellus shale. 



The base of the Hamilton series throughout Pennsylvania and New 



York is usually sharply defined by the base of the black Marcellus shale 

 which rests on a massive light grey limestone known as the Corniferous or 



shale — the Genesee. Some geologists have considered the Genesee shale or 



stone ranging from a few feet to thirty-five or more feet in thickness. 3 The 



valley, but apparently the limestone and shale do not extend to the east of 



1 See Dana's Manual of Geology, 4th ed., 189r>, p. 002. Prof. H. S. Williams, as reporter of the American sub committee on 

 the Upper Palaeozoic (Devonic) for the International Congress of Geologists, said : "There can be no reason whateverfordividing 

 the Genesee from the Portage, for in the typical section recurrences of the Genesee lithological conditions occur up to the very 

 base of the Portage sandstones, which terminate the Portage group of thi- New York system." (Congres •Geologique Interna- 

 tionale. Compte Rendu, 4 mc Sese., 1891, Appendix A, p. 143 [p. C 23 of the copies printed in 1888 by the American committee]. 

 Also see p. A 145.) Professor Williams was also inclined to refer the Tully limestone to the Portage, for he said : "In order to 

 adapt our usage to the accepted us;)ge of European standards, when speaking of Upper and Middle Devonian, we should include in 

 the Upper Devonian the Genesee shale and so much of the Tully as contains the Rhynchonella venustula fauna." (Ibid., and see 

 p. A 145.) This opinion was also advanced by Professor Williams in his paper on " The Cuboides Zone and Its Fauna ;>a Dis- 

 cussion of Methods of Correlation," where he concludes with the following statement : " Therefore, if we wish to express precise 

 correlation in our classification of American rocks, the line between Middle and Upper [Hamilton and Chemung] Devonian forma- 

 tions should be drawn at the base of the Tully limestone, to correspond with the usage of French, Belgian, German and Russian 

 geologists." (Bulletin Geological Society America, Vol. I, May. 1890, p. 499.) 



2 For the western limit of the Tully limestone see Professor Hall's statement: " This rock is virtually absent at all places west 

 of Canandaigua lake " (Geology of New York, Part IV.. 1813, p. 213). Also the Geological Map of Ontario county, New York, by 

 J. M. Clarke, on which it is represented as not reaching Canandaigua lake. The author says "the rock disappears entirely in 

 Gorham some miles before reaching the east shore of Canandaigua lake " (Report State Geologist [New York] for 1884, 1885, p. Wi- 

 lt has more recently been shown by D. D. Luther, that the westernmost outcrop of this limestone is about one mile from Gage's 

 Landing, on the east shore of the lake mentioned, and that its place in the rock series from this point westward to Erie county is 

 taken by a thin stratum of iron pyrites (Thirteenth Report State Geologist [New York] for the year 1893. Vol I., pp. 38 42, 1894). 



3 Professor II. S. Williams says: " From a few feet to over fifty feet " (Bulletin Geological Society of America, Vol. I., p 487'. 

 Professor S. G. Williams gave the greatest thickness as on Skaneateles lake, where he measured two sections, one twenty-five feet 

 four inches, the other twenty-eight feet two inches, and at Tinker's Falls, " twenty-six or thirty-seven and one-half feet, accord- 

 ing as one includes or excludes the impure mixed top and bottom portions " (Sixth Annual Report State Geologist [New York] 

 for 1886, 1887, p. 20). 



Genesee slate accompanies the Tully limestone as far eastward as the Chenango 



