230 PALEOZOIC TIME. 



According to Salter, a number of species of the Upper Silurian, and probably of this 

 part of it, have been observed in Arctic rocks ; as, Halysites catenulata, Orthis eleyantula, 

 Favosites Gothlandica, Leperditia BalticaHismg., species of Calophyllum, Heliolites, Cysti- 

 phyllum, Cyathophyllum, Syrinffopora, with Pentamerus conchidium Dalm., Atrypa retic- 

 ularis, etc.; and, at the southern extremity of Hudson's Bay, Pentamerus ublonyus, 

 Atrypa reticularis, etc. About Lake Winnipeg, also, Upper Silurian fossils have been 

 found. See Am. Jour. Sci., II. xxi. 313, xxvi. 119. 



The fossils of the Coralline limestone (p. 222), as Hall states, are mostly peculiar to 

 it. Out of thirty-two species (including Corals, Brachiopods, Conchifers, Gasteropods, 

 Cephalopods, and Crustaceans) only the following are set down as identical with Niagara 

 fossils: Stromatopora concentrica, Favosites Niagarensis, Halysites catenulata, Spirifer 

 crispus, Rhynchonella lamellataH.; and these are not all beyond doubt. Moreover, three 

 of them are cosmopolite species. The beds are, therefore, strikingly different in life from 

 the Niagara, and may represent a later epoch. Among the species, there are very 

 large spiral chambered shells, of the genus Trochoceras Hall, which are unknown in 

 other formations. 



General Observations on the Niagara Period. 



Geography. — The facts upon which rest the conclusions with regard 

 to the geography of the Niagara period are, — 



1st. The occurrence of the Oneida conglomerate over the region 

 from central New York southward, through the length of the Appa- 

 lachians, instead of extending eastward to the Hudson River. 



2d. The Medina sandstone covering the same region, but spreading 

 farther westward on the north. 



3d. The Clinton group having the same range on the east, and ex- 

 tending over a considerable part of the interior basin to the Missis- 

 sippi ; shales characterizing the formation in the Appalachian region, 

 shales and sandstones prevailing over limestones in New York, and 

 limestones, more or less argillaceous, mostly constituting the beds in 

 the West. 



4th. The Niagara rocks, stretching farther east, but thinning out on 

 the Hudson River, and thickening westward ; spreading over the Ap- 

 palachian region, and also through a large part of the Interior basin ; 

 consisting of shales with some limestone in central New York, more 

 limestone in the western part of the State, shales almost solely in the 

 Appalachian region, limestones in the Interior basin. 



5th. The formations six to eight times thicker in the Appalachian 

 region than in the West. 



6th. The Niagara limestone existing in the Eastern-Border region, 

 eastward of northern Vermont, to Gaspe ; and the whole period rep- 

 resented in Anticosti by limestone. 



The position of the coarse conglomerate rocks of the Oneida epoch, 

 spreading over neither eastern New York nor the Interior basin west 

 of the State, apparently indicates that along its line was the sea-coast 

 of the time, and that the ocean reached it in full force. Such coarse 

 beds of marine formation are formed either in front of the waves, or 



