PALEOZOIC TIME — DEVONIAN. 603 



the Tully limestone, and 25 feet on Lake Erie, and 200 to 300 in west central 

 Pennsylvania. Along one or two levels there are great numbers of large 

 and small calcareous concretions which are often septate (page 97), so as 

 to make the concretions look a little like the backs of turtles. In western 

 New York a layer of bituminous limestone, six inches to two feet thick, 

 occurs near the middle, which is mostly made up of shells of a Pteropod, 

 the Styliolina jissurella Hall (Fig. 916), and is called the StylioUna lime- 

 stone. With it occur remains of fossil fishes, Dinichtliys, Palceoniscus, and 

 other species. 



The Portage group, of New York (so named from the village of Portage, 

 Livingston County, N.Y.), outcrops along a wide belt extending eastward 

 from the south shore of Lake Erie. It is well displayed about the south 

 end of Cayuga and Seneca lakes. Its beds are shales and flags, or shaly 

 sandstones, — the Naples group, — and, above these, the Portage sandstone, 

 which has relations to the Chemung. The rocks have a thickness of 1000 

 feet on the Genesee River, and 1300 to 1400 near Lake Erie. The rocks are 

 in general very sparingly fossiliferous. They abound in ripple-marks and 

 mud-cracks, and the sandstones are often cross-bedded. But a portion in 

 central New York, called the Ithaca group, — prominently displayed on the 

 Cascadilla and Fall creeks, near Ithaca, — abounds in fossils. According to 

 H. S. Williams, the fossils, which are largely Brachiopods, have near relations 

 to those of the Chemung group, and also about as close to Hamilton species ; 

 and as they are overlaid by 500 or 600 feet of sandstones, mostly barren, but 

 containing some Portage species, they are referred to the Portage group. 

 They are the only part of the beds that give much knowledge of the life 

 of the period ; and this is imperfect, as Trilobites, Corals, Crinoids, and other 

 species of purer waters, are absent. 



In eastern central New York, in Delaware, Otsego, and Chemung counties, 

 there is a sandstone formation, the Oneonta sandstone of Vanuxem, which 

 resembles the Catskill beds ; but it is overlaid by beds containing Portage 

 fossils ; and in some places, Chemung species. It indicates the existence, 

 at these localities, of Catskill conditions during the Portage and Chemung 

 epochs, if not also during part of the Hamilton period. (H. S. Williams.) 

 On the distribution of the Oneonta beds, see Darton, Am. Jour. Sc, 1893. 



In central and western Pennsylvania the limit between the Portage and 

 Chemung is not clearly ascertained. The thickness of the two in Monroe 

 County, eastern Pennsylvania, is about 2500 feet ; Fulton County, south 

 central Pennsylvania, about 3600 feet, of which 400 are referred to the 

 Portage. Along the south shore of Lake Erie, the lower part of the " Ohio 

 shales " is referred to the Portage, and the rest to the Chemung. Near 

 Cleveland, 0., the thickness of the "Ohio shales" is about 1350 feet, and 

 farther west, at Elyria, 950 ; but at Wellsville on the Ohio, 2600 feet. 



The Chemung beds in New York are a continuation of the Portage, with 

 little change in the rocks, except that they are slightly more arenaceous, 

 and of a lighter color, but with a great change in the abundance of fossils and 



