596 



HISTORICAL GEOLOGY. 



3. Equiseta or Horse-tails. — Calamites (named from calamus, a reed, in 

 allusion to their reed-like or rush-like aspect) are ancient Equiseta. Fig. 

 900 represents a portion of a stem (in horizontal position) flattened out by 



900. 



Fig. 900, Archaeocalamites radiatus ; 901, Asterophyllites latifolius. Dawson. 



pressure. It shows that the Devonian species of the tribe exceeded much in 

 size the modern species ; as in recent kinds, the stems were jointed (ab). A 

 plant of the same tribe, called Asterophyllites (because of the arrangement of 

 the leaves in stars), is represented in Fig. 901. 



4. Gjnnnosperms. — Gymnosperms were represented by species of the 

 Yew family (Taxinese), and by leaves of plants of the tribe of Cycads. 

 Trunks a foot in diameter, of the former, occur in the black shale of the 

 Hamilton, and others as large, or larger, in the ISTew Brunswick beds. Most 

 of the latter are referred by Dawson to the genus Dadoxylon. To the Cycad 

 family belongs the Cordaites Rohhii, a leaf of which, from a cluster figured 

 by Dawson, is represented in Fig. 896. It is questioned whether leaves like 

 those of ArcJioiopteris may not be from a related Cycadean, as one genus of 

 modern Cycads, Strangeria, has fern-like leaves (Williamson). Fossil nuts 

 were found with the specimen of C. Rohhii, which "may have belonged to 

 it" (Dawson). 



5. Sporangites. — Spore-cases and spores are abundant in the black Mar- 

 cellus shale of New York and Pennsylvania, and are a prominent source 

 of its bituminous character. They are usually minute black shining spots in 

 the shale. 



Animals. — The animal remains of the Marcellus are comparatively 

 few, and, excepting the Cephalopods, generally small. Their small number 

 corresponds with the fact that the rock is a fine shale. In the Hamilton 

 beds, which are coarser, and often resemble a consolidated mud-bed, fossils 

 are much more numerous; but Lamellibranchs and Brachiopods are most 

 abundant, as is usual in impure waters. 



1. Spongiozoans. — A Middle Devonian species of Sphoerospongia, first 

 described by Phillips from British specimens, is represented in Figs. 902 a, b, 



