

LOWER SILURIAN. 195 



the Archaean farther north. The shale is in some places three hundred 

 feet, or more, thick. It extends westward through Canada, and 

 beyond, probably into Wisconsin and Iowa, though a very thin de- 

 posit at the west ; and also southward along the Appalachians, being, 

 in Pennsylvania, from three hundred to seven hundred feet thick. 



The rock is a crumbling shale, mostly of a dark blue-black or 

 brownish-black color, and frequently bituminous or carbonaceous, — 

 so much so, in certain places, as to serve as a black pigment. It 

 sometimes contains thin coaly seams; and much money has been 

 foolishly spent in searching for coal in this deposit. Thin layers of 

 limestone are occasionally interpolated, especially in the lower part. 



The rocks of the Hudson River epoch are shales in New York and 

 Canada, but become calcareous to the west, and consist of limestone, 

 largely mingled with shale, about Cincinnati, in Ohio, and farther west. 

 The shales in New York (called Hudson River and Lorraine shales) 

 cover a narrow area through the centre of the State, near the Mohawk, 

 which widens toward the Hudson, and extends down the Hudson to 

 Fishkill and Newburg ; fossils have been found in them near Pough- 

 keepsie. West of New York, the shales extend through western 

 Canada, and southward of the State, along the Appalachians. The 

 greatest thickness in Central New York is 1,000 feet. The Cincin- 

 nati limestone continues from Ohio westward, outcropping in several 

 of the States of the Mississippi valley. 



Limestone of this epoch occurs on the Island of Anticosti, in the 

 Gulf of St. Lawrence, about 1,000 feet thick. 



The slates of the Taconic Mountains of Western New England and 

 the eastern border of New York, which include argillyte, hydromica, 

 mica, and chlorite schists, being increasingly crystalline to the south- 

 ward, are underlaid by the crystalline limestone adjoining; and it 

 has been proved by fossils, both in Vermont and in New York, that 

 the limestone adjoining the slates is in part Tre'nton. The slates are 

 Hudson River. These " Taconic slates " are continuous with the 

 Poughkeepsie slates above referred to. (See beyond, p. 212.) 



1. Trenton Epoch (a.) New York and to the Eastward. — In New York, the 



Trenton limestone is grayish-black to black. It is sometimes bituminous, especially in 

 its upper portions. Its layers are often thin, and beds of shale in many places inter- 

 vene. The black color is due to carbon or carbonaceous substances, as is shown by its 

 burning white. The crystalline points of the Birdseye are not always present, and occur 

 in other limestones. The color of this rock is drab or dove-colored and brownish, and 

 not so dark as that of the overlying beds. The Black River limestone is named from 

 Black River, N. Y., east of Lake Ontario. The color is generally dark, nearly black. 



In Canada, the Trenton outcrops over a large area about Ottawa, and also over an- 

 other of less width along the north side of the St. Lawrence, from Montreal eastward 

 nearly to Quebec, and at intervals beyond to Murray Bay ; and a branch passes south- 

 ward from Montreal to Lake Champlain. Near Montreal, the whole thickness is 530 

 feet, and that of the lower part, including the Black River limestone and Birdseye 

 limestone, 38 feet (Logan). 



