CHARACTER AND DISTRIBUTION 947 



Two miles south of the mouth of Eighteen Mile Creek the Genesee 

 shale has a thickness of 12 inches and is followed by the Styliolina (Gen- 

 undewa) limestone, the conodont phase being absent. Farther east, in 

 Erie County, this shale thickens. Thus at Spring Brook it is from 19 to 

 26 inches thick and increases regularly east of this point. 



West of Buffalo both the TuUy and the Genesee are absent, and the 

 Portage shales lie with a disconformable contact on the eroded surface of 

 the Upper Hamilton. In western Ontario the beds above the Morse Creek 

 limestone (the equivalent of the Ludlow ville and Moscow shales of central 

 New York) thicken to 150 feet, but in northern Ohio erosion in Upper 

 Devonic time had removed all the beds above the Prout limestone, the 

 probable equivalent, according to Stauffer, of the Encrinal (Morse Creek) 

 limestone of western New York. This erosion occurred, of course, prior 

 to the deposition of the black Portage (Ohio) shales. The disconformity 

 between the Ohio (Portage) shales and the Hamilton beds is traceable 

 throughout Ohio, Indiana, Kentuck}-, Michigan, Wisconsin, Illinois, and 

 westward, becoming in general greater toward the south. This implies, 

 then, that during early Upper Devonic time — that is, during the period 

 of deposition of the Tully and the Genesee of New York — the region west 

 of New York was dry land and subject to erosion. 



In the Genesee Valley the Tully is represented by a pyrite layer a few 

 inches in thickness, which contains the dwarfed fauna described by 

 Loomis.* This fauna still shows nearly 75 per cent of Hamilton species, 

 all, however, occurring as dwarfed varieties and which were clearly de- 

 rived from the rich Hamilton fauna of the underlying Moscow shales, 

 though their size averages only one-fifteenth that of the normal. The 

 Genesee shale here is 82 feet thick, and the pyrite layer marks the final 

 change in sedimentation, although the upper four or five feet of the Mos- 

 cow show a transition from the open and pure-water condition, in which 

 the rich Hamilton fauna lived to a muddy sea, with a much reduced 

 fauna. The pyrite layer finally marks the development of shallow pools 

 with stagnant water and the liberation of much sulphur ; but these pools 

 were later destroyed by the influx of the black muds, which constitute the 

 Genesee formation. As has been noted al)ove, this pyrite layer can be 

 traced west into Erie County. 



The Tully limestone of the type region is for the most part a bedded cal- 

 cilutyte, in which fossils occur sporadically, but are on the whole rather 

 infrequent. A noteworthy fact is that the fossils that do occur are all 



* New York State Museum. Report of the State Paleontologist for 1902, pp. 892-920, 

 with plates ; 1903. 



LXX — Bull. Geol. Soc. Am., Vol. 28, 1916 



