HAMILTON PERIOD. 281 



I. Rocks : kinds and distribution. 



The rocks in the eastern United States are either shales or sand- 

 stones, with some thin limestone beds. Shales especially abound 

 in the State of 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 con- 

 tains traces of coal or bitumen, so as sometimes to afford flame in 

 the fire. The Hamilton beds (10 I) in New York (so named from 

 Hamilton, Madison co., 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-Eiver 

 flags, comes from a thin layer in the Hamilton. The Genesee shale 

 (10 c) is a blackish 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 1200 feet — is east of the centre 

 of the State. It extends southwest into Pennsylvania and Vir- 

 ginia, and also westward, as a thin rock, mainly of limestone, 

 through parts of Michigan (at Mackinac), Illinois (at Eock Island, 

 etc.), Iowa (New Buffalo, etc.), Missouri, and elsewhere. Beds 

 probably of this period occur also in Maine, and near Gaspe. 



(a.) Interior Continental basin. — In the lower part of the Marcellus shale (the 

 rock of the first epoch) in New York, there are also layers of concretions of 

 impure limestone, and these abound most in fossils. But the fossils of the 

 shale are generally small. 



The Hamilton beds consist of shales separated into two parts by a thin layer 

 of Encrinal limestone, and in many places overlaid by a thin limestone stratum 

 called the Tully limestone. In the 



annexed section from the coast of j^ 432, 



Lake Erie (as given by Hall), the 

 Hamilton beds, 10 b, include (1) blue 

 shale j (2) Encrinal limestone; (3) 

 Upper or Moscow shale : the Tully 

 limestone is wanting. Above lie 

 (10c) the G-enesee slate; and (11) a 

 part of the Portage group of the Section of Hamilton beds, Lake Erie, 



next (Chemung) period. 



The flagging-stone of the Hamilton is quarried near Kingston, Saugerties, 

 Coxsackie, and elsewhere on the Hudson in Ulster, Greene, and Albany cos., 

 N.Y., and also near Cayuga Lake. The bed is but a few feet thick. It breaks 

 into very even slabs of great size. It is almost without fossils, but is penetrated 

 in many parts by the filling of a slender worm-hole. The Genesee slate overlies 

 the Tully limestone when this is present. It is not recognized in the eastern 

 part of the State of New York. 



