RELATIVE GEOLOGICAL ANTIQUITY OF TREES. 133 



water, carbonic acid, ammonia, and certain salts ; animals, on 

 the contrary, require plants and other animals for their ex- 

 istence. Such a soil forms itself only in the course of ages, 

 out of the underlying rocks. Through the chemical influence 

 of the air, and the solvent and mechanical power of the rains, 

 the rocky surface was gradually broken up, and the loose 

 material was either left lying on the surface, or, driven along 

 by torrents of water, was deposited in other places at a dist- 

 ance. Eocks composed of matter which has thus been de- 

 posited from water are called sedimentary rocks, and we find 

 first in the most ancient of these rocks the remains of plants 

 and animals, the so-called fossils. 



The time occupied in the formation of these ancient deposits 

 is called for this reason by Geologists the Palaeozoic period, 

 because they contain the first germs of higher organic forms, 

 and are the repository of its most ancient life. The Cambrian, 

 Silurian, and Devonian formations are the oldest historical 

 rocks, and the fossils which they contain prove that the earth 

 was at this time no Eden, but, on the contrary, a monstrous 

 muddy swamp. Water appears to have predominated over 

 the land. Among animals the fish held the highest rank. 

 There was an abundance of shell-fish and corals, and a crusta- 

 ceous swimming animal called a trilobite. The air contained 

 a great amount of carbonic acid gas. 



The plants belong to the Cryptogamous or flowerless divi- 

 sion, and are decidedly low in organization. They consist of 

 gigantic calamites, plants allied to the horsetail (Eguisetum) } 

 ferns, and arborescent club-mosses (Lycopodium), called Lepi- 

 dodendra in fact, such plants as are found now in swamps, 

 and whose size is at present very diminutive. AD al- 

 most endless ocean yet covered the earth's surface. Only 

 here and there an island was visible, rugged and torn, and 

 which the first offspring of the young creation covered. Land 

 was, indeed, created, and the waves of these ancient seas broke 

 against the rocks as now, and plowed out for themselves gulfs 

 and bays. In the interior of the earth the wild efforts and 

 strength of the fire had, in some measure, abated. The vol- 

 canoes were less numerous. Yet the blue heavens were not 



