64 



they oppose the inroads of cultivation, and pre* 

 serve, like inland gulfs, the stability of their 

 boundaries. I will not touch upon the great 

 question, whether in the Sahara, that Mediter- 

 ranean of moving sands, the germs of organic 

 life are increased in our days. In proportion as 

 our geographical knowledge has extended, we 

 see in the eastern part of the desert islets of 

 verdure, oases covered with date-trees, crowd 

 together in more numerous archipelagoes, and 

 open their ports to the caravans ; but we are 

 ignorant whether the form of the oases have not 

 remained constantly the same since the time 

 of Herodotus. Our annals are too incomplete 

 and too short, to follow Nature in her slow and 

 progressive progress. From these spaces en- 

 tirely bare, whence some violent catastrophe 

 has swept away the vegetable covering and the 

 mould ; from those deserts of Syria and Africa, 

 which, by their petrified wood, attest the changes 

 they have undergone ; let us now turn our eyes 

 to the llanos covered with grasses, to the dis- 

 cussion of phenomena that come nearer the 

 circle of our daily observations. The planters 

 settled in the steppes of America have formed 

 respecting the possibility of a more general 

 cultivation the same opinions ; as those which 

 I deduced from the climatic action of these 

 steppes considered as surfaces, or continuous 

 masses. They have observed, that downs en- 



