120 French Scientific Mission to the Pampa del Sacramento. 
fertile, abounding in those three grand elements of fertility, 
heat, moisture, and a deep alluvial soil. The vast volumes 
of water drawn up by the tropical heats from both oceans, 
and the rarefaction of the atmosphere over the heated plains, 
landward, produce rainy seasons of extraordinary intensity, 
and to this must be added the floods caused by the melting 
of the snows. Of the vast basins formed by the streams that 
flow into the Atlantic, those to the north and south of that of 
the Amazon and its tributaries, receive a less amount of 
rain, and consist of the richest prairies as well as of wood ; 
but that of the Amazon, being the most extensive of all, is 
so charged with moisture and heat, as to be covered through- 
out its whole extent with stupendous trees, and a thick un- 
dergrowth of shrubs and parasitic plants, so as to be in many 
places almost impenetrable, and extremely unhealthy. No 
wonder that the upper parts of this, the largest forest in the 
world, separated from the Spanish colonies on the Pacifie by 
the tremendous barrier of the Andes, and remote from the 
chain of European settlements on the Atlantic sea-board, 
should be still very imperfectly known. This is the region 
which M. Castelnau and his companions were commissioned 
to explore. 
Thinly scattered as is the present Indian population of this 
extensive basin, it may be expected one day to be as prolific 
in human beings as it is now in the noblest productions of 
vegetable life, and in wild beasts, birds, and fishes. Indeed, 
on comparing the descriptions given us by Humboldt of the 
three great basins drained by the Oroonoko, the Amazon, 
and the Rio Plata, it would seem as if the first and the last 
were best suited to herbivorous animals, the horse, the ox, 
and the sheep; while the central one may ultimately prove 
the most abundant in providing for the sustenance and con- 
venience of man. Humboldt’s description forms an interest- 
ing preparative for the story of this French expedition, and 
we therefore give it entire. 
“ These three transverse chains, or rather the three groups 
of mountains, stretching from west to east,—that is, from 
the great chain of the Andes to the Atlantic, within the limits 
of the torrid zone, are separated by tracts entirely level, the 
