238 GEOLOGY. 



342. Triassic Salt. While in this country the chief 

 source of salt is in the Silurian formation ( 278), in En- 

 gland and Europe it is in the Triassic system, which is 

 often, for that reason, called the Saliferous system. The 

 rocks in connection with which the salt is found are sim- 

 ilar in both formations, but the manner in which the 

 salt was produced could not be the same in both cases. 

 The evaporating process which it is supposed, as stated 

 in 278, produced it in the Silurian formation in New 

 York, could not in any way accumulate masses of rock 

 salt 40 yards in thickness, or a mountain of salt 600 feet 

 high and 1200 broad, such as is found at Cordova, in Spain, 

 It is supposed that volcanic agency operated in such 

 cases, as salt is common in what is thrown out from vol- 

 canoes, and salt-springs sometimes rise to the surface 

 from granitic rocks, showing that there are sources of 

 salt lying deep in the earth. The purity of the rock- 

 salt, it is thought, indicates its volcanic origin, for if it 

 were deposited from a solution it would have impurities 

 mingled with it. 



343. Plants of the Triassic Period. Though the plants 

 which were peculiar to the Carboniferous age were not 

 present, as the Sigillaria and the Lepidodendrons, yet 

 there were Cycads as there were then, and Ferns, Equi- 

 seta, and Conifers in new forms. Trunks of conifers of 

 considerable size have been met with in the sandstones. 

 Some coal has been found in this formation in some lo- 

 calities, made, of course, out of the vegetation of which I 

 have spoken. Triassic coal has been discovered in Vir- 

 ginia and North Carolina in this country, in Australia, 

 and in various parts of Asia. 



344. Animals. The excess of carbonic acid that ex- 

 isted in the atmosphere previous to the Carboniferous 

 age was removed from it by the rank vegetable growth 

 of that period, so that when the Triassic period came on 

 the air was fitted for air-breathing animals. They ac- 

 cordingly were introduced upon the scene. Not only 



