CAUSES OF IiAEGE FLAIA'S. 
07 
Fed sandstone, or on compact limestone and gypsum ; it 
on^tvf according as periodical inundations accumulate mud 
lower grounds, or as the shock of the waters carries 
from the small elevations the little soil that has covered 
em- Many solitary cultivated spots already exist in the 
'ust of the pastures, where running water, and tufts of 
^Yi?, ^^’ij’itia palm, have been found. These farms, sown 
sid^ and planted with cassava, will multiply con- 
erably if trees and shrubs bo augmented, 
sol 1 . excessive heat of the mesas do not depend 
tion f ^ the nature of tlieir surface, and the local reverbera- 
the soil ; their climate is modified by the adjacent 
j w'hole of the Llano of which they' form a part. 
the deserts of Africa, or Arabia, in the Llanos of South 
•vine- • - 
T '^®Fiea, in the vast heaths extending from the extremity ot 
]• to the mouth of the Scheldt, the stability of the 
ch' fl desert, the savannahs, and the downs, depends 
pi*, y on their immense extent, and the nakedness these 
Os have acquired from some revolution destructive of the 
oont^^^-' ^Setation of our planet. By their extent, their 
Vatj and their mass, tliey oppose the inroads of culti- 
^ou°*f! preserve, like inland giUfs, the stability of their 
ther • I ndll not enter upon the great question, whe- 
jTg tile Sahara, that Mediterranean of moving sands, the 
tion * org.anic life are increased in our days. In propor- 
djjjg °nr geographical knowledge has extended, we have 
oase eastern part of the desert islets of verdure, 
’’ous date-trees, crowd together in more nume- 
We . ’Polagos, and open their ports to the caravans ; but 
(.gjj Ignorant whether the form of the oases have not 
’Constantly the same since the time of Herodotus, 
ture **Fe too incomplete to enable us to follow Na- 
ontirT vf gradual progress. From these spaces 
""hence some violent catastrophe has swept 
serts i® covering and the mould; from those de- 
attest y Africa, which, by their petrified wood, 
grass-e ^^‘^nges they have undergone ; let us turn to the 
lhat c Llanos and to the considei’ation of phenomena 
circle of oim daily observations. He- . 
Ktepn-. ^ possibility of a more general cultivation of the 
^ us ot America, the colonists, settled there, concur in the 
■ III. TI 
