242 



PALEOZOIC TIME. 



River. It outcrops in Ohio, either side of the Lower Helderberg area, and extends 

 thence into Indiana. In southern Illinois, there are 250 to 300 feet of siliceous lime- 

 stones. In St. Genevieve County, Missouri, the rock is a limestone (Shumard). 



The Nova Scotia strata of this epoch occur at Nictaux and on Moose and Bear rivers. 

 They include a thick band of fossiliferous iron-ore, which is an argillaceous deposit at 

 Nictaux, but, owing to partial metamorphism, is magnetic iron- ore, and partly specu- 

 lar, on Moose River. At Gaspe, it includes the upper part of the limestone formation, 

 and probably the lower part of the sandstone beds, a Rensselaeria having been found 

 1,100 feet above the base of the sandstones. 



H. Life. 

 1. Plants. 



Sea-weeds are not uncommon. No remains of land-plants have yet 

 been observed in the beds of New York, or at the West. But, in the 

 upper limestones of Gaspe, remains of a small species of the Lycopo- 

 dium or Ground-Pine tribe occur, which have been named by Dawson 

 Psilophyton princeps, a figure of which is given on p. 258. The Ly- 

 copods are Cryptogams, or flowerless plants, but belong to the highest 

 division of Cryptogams, that of Acrogens. The plant grew to about 

 the same height with the common American species Lycopodium den- 

 droideum. (For further description, see p. 257.) 



2. Animals. 

 The most common Mollusks are the coarse Spirifer arenosus H. 

 (Fig. 475), and the Rensselaeria ovoides H. (Fig. 476.) The rock is 



Figs. 475-476. 



Brachiotods. —Figs. 475, 475a, Spirifer arenosus ; 476, Rensselaeria oroides. 



often made up of these large fossil shells crowded together, or con- 

 tains their moulds, with the cavities the shells once occupied. Fig. 



