NIAGARA PERIOD CLINTON EPOCH. 



235 



slope of the last main ridge of the foot of the Alleghany Mountains." (H, D. 

 Rogers.) 



c. Eastern border region. — The total thickness of the series of limestones at 

 Anticosti is 1344 feet. Of this, 734 feet have been supposed to " show a passage 

 from the Upper to the Lower Silurian." (J. Richardson, in Logan's Report.; 

 But according to Shaler, the whole series belongs to the Upper Silurian, and it 

 extends into the Niagara epoch. 



In Nova Scotia, as described by Dawson, the strata occur on the northern 

 coast. At Arisaig, where the rocks are shales and limestone and have a thick- 

 ness of about 500 feet, fossils occur through the formation and are very abundant 

 in the upper or more calcareous part. At the East River of Pictou there are 

 also slates and calcareous bands, probably of this epoch. They include a deposit 

 of oolitic iron-ore, like that of the Clinton rocks of central New York, which 

 in some places has a thickness of 40 feet. 



South of the St. Lawrence, Clinton beds occur on the river Chotte.. 



II. Life. 



The rocks of the Oneida and Medina epochs, as they afford but 

 few fossils, give no assurance that the waters had been fully resup- 

 plied with life after the destruction that closed the Lower Silurian. 

 But in the beds of the Clinton epoch fossils again abound, and the 

 Niagara strata, which follow, bear full testimony to a populous 

 globe. 



1. Plants. 



Great numbers of Fucoids occur in the Clinton beds of central 

 New York, differing from those below. They are of various dia- 

 meters, from the size of a finger and larger to 

 that of a thread. 



One of the most characteristic species is re- 

 presented in fig. 364. No traces of land-plants 

 are known. 



2. Animals. 



Many of the limestones were coral reefs, and 

 abound in corals, a few of which are repre- 

 sented in figs. 365-368. Graptolites (figs. 

 369, 369 a) continue in the waters over the 

 muddy bottoms, but the genus here became 

 extinct. Brachiopods were common: among 

 them the genus Pentamerus has here its earliest 

 species, and P. oblongus (fig. 371) was especially 

 abundant. The tracks of some of the Mollusks 

 are found on some layers. Fig. 381 is a portion 

 of one, reduced one-half: it resembles the track made in the mud 

 by some Unios. Fig. 382 represents what is supposed to be the 



Rusophycus bilobatus. 



