266 PALEOZOIC TIME. 



America, just illustrated, favors an approximate identity of climate :- 

 there is no sufficient evidence of any cold Arctic, or even of any wide 

 diversity of zones. 



2. HAMILTON PERIOD. (10.) 

 Epochs — 1. Marcellus, or that of the Marcellus shale (10 a) ;. 

 2. Hamilton, or that of the Hamilton beds (10 b) ; 3. Genesee, or 

 that of the, Genesee shale (10 c). 



I. Rocks: kinds and distribution. 



The rocks in New York and along the Appalachians are either 

 shales or sandstones, with some thin limestone beds. Shales especially 

 abound in New York. 



The Marcellus shale (10 a) is for the most part a soft, argillaceous 

 rock ; the lower part is black with carbonaceous matter, and contains 

 traces of coal or bitumen, so as sometimes to afford flame in the fire. 

 The Hamilton beds (10 b) in New York (so named from Hamilton, 

 Madison County, N. Y.) consist of shales and flags, with some thin 

 limestone beds. The excellent flagging-stone in common use in New 

 York and some adjoining States, often called North-River flags, comes 

 from a thin layer in the Hamilton. The Genesee shale (10 c) is a 

 blackish bituminous shaly rock, overlying the Hamilton. 



The Hamilton formation spreads across the State of New York, 

 having its northern limit along a line running eastward from Lake 

 Erie. The greatest thickness — about 1,200 feet — is found east of 

 the centre of the State. It extends southwest, into Pennsylvania and 

 Virginia ; also westward, as a thin rock, mainly of limestone, through 

 parts of Ohio, Michigan, and Illinois (at Rock Island, etc.), to Iowa 

 (New Buffalo, etc.) and Missouri. Following this limestone, in Ohio, 

 Indiana, and Illinois, there is what is called the Black shale (or Black 

 slate), corresponding apparently to the Genesee shale ; it occurs also in 

 Kentucky and Tennessee, but, although so wide spread, does not ex- 

 ceed 350 feet in thickness, and is usually about 100 feet. 



Hamilton beds occur also in the valley of the Mackenzie River, 

 between Clear Water River and the Arctic Ocean, some of the species 

 of fossils being identical with those of the United States and Canada ; 

 and, as stated by Meek, Devonian rocks are probably continuous, or 

 nearly so, from western Illinois northwesterly to the Arctic Ocean, a 

 distance of 2,500 miles. 



In the Eastern-border region, the Hamilton beds are chiefly sand- 

 stones, and are confined to regions near the sea-border. They occur 

 in Maine and New Brunswick, near the boundary between these 

 States, and beyond up the New Brunswick coast ; also at Gaspe, on 

 the Gulf of St. Lawrence. 



