218 PALAEOZOIC TIME — LOWER SILURIAN. 



stretches across the Ohio into Kentucky and Tennessee, and west- 

 ward into Illinois and Missouri. The greatest thickness in New 

 York is nearly 1000 feet; in the Northwest it is very thin. Along 

 the Appalachian region, in Pennsylvania, the rock is a shale, and 

 has a thickness of 1600 feet or more. 



In the Eastern border, at the island of Anticosti, the lower 

 part of a limestone formation has been referred to this period ; 

 but recent investigations discredit it. 



1. Utica Epoch. — (a.) Interior Continental basin. — The Utica shale is 15 

 to 35 feet thick at Glenn's Falls, in New York ; 250 feet in Montgomery co. ; 300 

 in Lewis co. 



(6.) Appalachian region. — In Pennsylvania, the rock is a hlack shale, and in 

 some parts it is fossiliferous. The thickness given by Professor Rogers in the 

 Kittatinny, Nippenose, and Nittany valleys is 300 feet, and in the Kischico- 

 quillas valley 400 feet. 



2. Hudson River Epoch. — (a.) Interior Continental basin. — The Hudson 

 River shales cover the region north of Lake Champlain, in Canada, west of the 

 great fault which marks the western boundary of the Calciferous beds (see map, 

 fig. 205), and they also lie over a small area near the centre of the Trenton 

 limestone region of the Ottawa basin. 



The thickness of the shales in Schoharie co., N.Y., is 700 feet (Vanuxem) ; 

 on Lake Huron, 180 feet (Logan) ; in the Michigan peninsula, 18 feet (Win- 

 chell); in Iowa, 25 to 100 feet (Hall & Whitney). In Missouri, there are alter- 

 nating strata of shale and limestone, 20 feet and less to 60 feet thick, the Avhole 

 120 feet in thickness (Swallow). In central Tennessee, the beds constitute 

 part of the Nashville group of Safford (the lower part being Trenton), and 

 consist of argillaceous limestone with many shaly layers : they are a few 

 hundred feet thick. 



(b.) Appalachian region. — In Pennsylvania, in the Kishicoquillas valley, the 

 rock is a blue shale and slate, with some thin layers of calcareous sandstone, 

 and the thickness is 1200 feet; in the Nittany valley, 700 feet; in the Nippe- 

 nose valley, a little less. (Rogers.) In eastern Tennessee, the beds (corre- 

 sponding to both the Utica and Hudson River epochs) are of great extent, and 

 consist of calcareous and more or less sandy shales, abounding at times in 

 Graptolites, with some thin layers of calcareous sandstone. They also occur 

 of great thickness in Virginia, and reach down to Alabama. 



(c.) Eastern border. — The limestone formation of the island of Anticosti, re- 

 ferred to the Hudson period, has a thickness of nearly 1000 feet. The limestone 

 is often impure, and is interstratified to some extent with shales. The strata are 

 nearly horizontal. 



3. Minerals. — In the Utica shale, near Spraker's Basin, there is 

 some lead-ore (galena) in small veins occupying the joints of the 

 rock. Mr. Whitney has called attention to the large amount of 

 carbon in the Hudson River shales from New York to Iowa, and 

 its economical importance. In the rock near Savannah, Illinois, 



