20 



the only plants we see on this arid rock, being plants whicfe 

 draw their nourishment rather from the air than from the 

 soil in which they grow." He also remarks, " It is not, in 

 general, by mosses and lichens that vegetation in the coun- 

 tries near the tropics begins. In the Canary Islands, as 

 well as in Guinea and in the rocky coasts of Peru, the first 

 vegetables that prepare the mould for others are the suc- 

 culent plants." 



These interesting observations, taken into consideration, 

 with the appearances yielded by the fossils accompanying 

 coal, lead to the further consideration of the formation of 

 that substance. From its chemical characters, its bearing 

 the impressions of vegetables, and being surrounded with 

 vegetable remains in the roofs and floors of the mines and 

 the accompanying coal-measures, its vegetable origin, it is 

 presumed, may be fairly inferred. The examination of the 

 various fossil vegetables which accompany it has deter- 

 mined that they chiefly belong to the grasses, reeds, the 

 cryptogamous and the succulent plants ; and point out the 

 kind of vegetables which most abounded, and, perhaps, to 

 the exclusion of trees and arborescent plants, at that period 

 when the land first escaped from the dominion of the 

 waters. It is true, that an exact agreement between the 

 forms and markings of these fossil remains, and of those 

 of the succulent plants which are offered to our observation 

 in the present day, is not often observable ; but it should 

 be considered that analogy will not authorise the ex- 

 pectation of an exact agreement, since it is rarely to be 

 found between the fossil remains and the animals now 

 existing, owing to fhe extinction of whole tribes from which 

 those fossil remains have proceeded. Besides, considerable 

 differences must result from the greater size observable in. 

 the fossil vegetables, especiallj^ in those of the succulent 

 tribe, than in those of more modern creation. Nor should 

 the differences be unnoticed which depend on situation and 



