PHYSICAL GEOGRAPHY. 
405 
From about 4° north latitude to 20° south, every stream 
that flows down the eastern slope of the Andes, is a tri- 
butary of the Amazon. This is as if every river, from 
St. Petersburg to Madrid, united their waters into one 
mighty flood. 
The Marahon, which is generally considered the main 
stream of the Amazon, deserves that title on several ac- 
counts. It rises to the westward of all the other great 
tributaries, and it receives all the waters which flow 
nearest to the Pacific, and most remote in a direct line 
from the mouth of the river. It flows for a consider- 
able distance in the most westerly valley of the Andes, 
separated by one range only from the Pacific, and at 
the point where it breaks through the eastern chain of 
the Andes, in 7 8° west longitude, is abeady a large river, 
on a meridian where all the other streams which can lay 
a claim to be considered the head- waters of the Ama- 
zon have as yet no existence. On going up the Ama- 
zon from its mouth, it is that branch on which you can- 
keep longest in the general east and west direction of 
the river ; and if the actual length of its course is con- 
sidered, it still keeps its place, for I find that there is 
not more than ten or twenty miles’ difference between it 
and the Uaycali, reckoning to the most distant source 
of the latter ; and its course is at present so uncertain, 
that future surveys may increase or diminish it conside- 
rably. 
These considerations, I think, decide the question as 
to the propriety of considering the Mar anon as the true 
source of the Amazon. We find that from its origin in 
the Lake Lauricocha, to its mouth in longitude 50° wcsL 
