276 PALEOZOIC TIME. 



Life. — The land plants of the Hamilton beds prove that, over the 

 rocks and soil of the emerged continent, with its islands, there were 

 forests and jungles of Conifers, Sigillarids, Lepidodendrids, Calamites, 

 and Tree-ferns. As to animal life, the Hamilton beds give us the 

 first evidence that the sub-kingdom of Articulates contained terrestrial 

 species. It is altogether probable that, besides Insects, there were 

 also Myriapods (Centipeds), and Spiders, the other kinds of terrestrial 

 Articulates. All these types may have appeared much earlier, with 

 the terrestrial vegetation of the Upper Silurian ; but there is as yet no 

 positive assurance of this. 



3. CHEMUNG PERIOD (11). 

 Epochs. — 1. Portage, or that of the Portage group (11a); 

 2. Chemung, or that of the Chemung group (11 b). 



I. Rocks: kinds and distribution. 



The Portage group in New York consists of shales and laminated 

 or shaly sandstones. Westward, the shales increase in proportion, 

 and eastward the sandstones ; and there are changes in the fossils, cor- 

 responding with these variations. The rocks have a thickness of 

 1,000 feet on the Genesee River, and 1,400 near Lake Erie. (Hall.) 

 They are well developed about Cayuga Lake, but have not been rec- 

 ognized in the eastern half of the State of New York. 



The Chemung group extends widely over the southern tier of 

 counties of New York, and consists of sandstones and coarse shales, in 

 various alternations. The thickness has been estimated at 1,500 feet 

 near the longitude of Cayuga Lake, and less toward Lake Erie and 

 beyond. 



Rocks of this period fail over a large part of the Interior Basin, 

 nothing intervening between the Black shale and the Subcarboniferous. 



To the south and southwest of New' York, in Pennsylvania, and 

 beyond along the Appalachian region, the corresponding beds have 

 great thickness, amounting in some places to more than 3,000 feet. 

 They are sandstones, as in New York. The upper part of the sand- 

 stone beds about Gaspe are referred to this period; and also the 

 plant-bearing beds at Perry, Maine. 



The beds in New York abound in ripple-marks, obliquely-laminated 

 layers, mud-marks and cracks from sun-drying, — evidences of the 

 existence of extensive exposed mud-flats, of sandy or muddy areas 

 swept by the waves, and of tidal currents in contrary movement 

 through the shallow waters. 



In western New York, the lower beds are the Cashaqua shales ; next, the Gardeau 

 shales and flags ; then, above these, the Portage sandstones. 



