784 



THE WONDERS OF GEOLOGY. Lect. VIII. 



the rashness of such generalizations." But though the 

 Silurian strata in Europe contain no vegetables but 

 fucoids, and these also abound in the equivalent deposits 

 in North America,* yet we have undoubted evidence that 

 in the " Hamilton group" of the United States — a series of 

 beds that corresponds in many of its fossils with the Lud- 

 low rocks of England — plants allied to the common carbo- 

 niferous type, as for example the Lepidodendra, are 

 abundant ; and in the lowest Devonian strata of New York, 

 the same plants occur associated with ferns. t 



Mr. Lyell also remarks, that as there is every reason to 

 conclude that the Silurian deposits were generally formed 

 far from land, this circumstance would alone explain the 

 extreme scarcity of terrestrial plants. The observations of 

 Professor E. Forbes on the physical conditions under 

 which the Silurian strata were deposited, tend to confirm 

 this opinion. This profound observer infers that the 

 Silurian seas, in those areas hitherto examined, were at 

 first very deep and tranquil, and afterwards that certain 

 areas became shallower, either from the accumulation of 

 detritus, or the partial elevation of the sea-bottom ; and 

 this opinion is based upon the following data, namely, the 

 small size of most of the conchifera — the paucity of spiral 

 univalve shells — the great number of floating mollusca, 

 such as the Bellerophon (Medals, p. 476), Orthoceras 

 (Medals, p. 484), &c. — the abundance of brachiopodous 

 shells (Spirifer, Leptcena, Or this, &c.) — the extreme rarity 

 of the remains of fishes — the deep-water forms of most of 

 the fucoids — and lastly, the absence of terrestrial plants. J 



19. Silurian Zoophytes and Mollusca. — The fossil 

 corals, crinoidea, and shells, in many of the Silurian rocks, 

 are so numerous, and comprise so many interesting forms, 



* See Medals of Creation, p. 105. 



f Mr. Lyell's Travels in America. X Ibid. p. 57. 



