id outlet is confined to the tributaries, nearly all of them,
like "the disembogning Nile," emptying themselves by innumerable
embouchures. To several tributaries the Amazon gives water before it
receives their tribute. Thus, by ascending the Negro sixty miles, we
have the singular spectacle of water pouring in from the Amazon through
the Guariba Channel.

The waters of this great river system are of divers tints. The Amazon,
as it leaps from the Andes, and as far down as the Ucayali, is blue,
passing into a clear olive-green; likewise the Pastassa, Huallaga,
Tapajos, Xingu, and Tocantins. Below the Ucayali it is of a pale,
yellowish olive; the Madeira,[154] Purus, Jurua, Jutahi, Javari,
Ucayali, Napo, Ica, and Japura are of similar color. The Negro, Coary,
and Teffe are black. Humboldt observes that "a cooler atmosphere, fewer
musquitoes, greater salubrity, and absence of crocodiles, as also of
fish, mark the region of these black rivers." This is not altogether
true. The Amazon throughout is healthy, being swept by the trade-winds.
The branches, which are not so constantly refreshed by the ocean
breezes, are occasionally malarious; the "white-water" tributaries,
except when they have a slack current in the dry season, have the best
reputation, while intermittent fevers are nearly confined to the
dark-colored streams. Much of the sickness on these tropical waters,
however, is due to exposure and want of proper food rather than to the
climate. The river system of South America will favorably compare, in
point of salubrity, with the river system of its continental
neighbor.[155]

[Footnote 154: The Madeira has often a milky color which it receives
from the white clay along its banks.]

[Footnote 155: The average temperature of the water in the Lower Amazon
is 81 deg., that of the air being a little less. The temperature of the
Huallaga at Yurimaguas was 75 deg. when the air was 88 deg. in the shade; in
another experiment both the river and air were 80 deg.. The Maranon at
Iquitos was 79 deg. when the air was 90 deg.. At the mouth of the Jurua, Herndon
found both water and air 82 deg.. In the tropics the difference between the
temperature of the water and air is proportionally less than in high
latitudes.]

As we might expect, the volume of the Amazon is beyond all parallel.
Half a million cubic feet of water pour through the narrows of Obidos
every second, and fresh water may be taken up from the Atlantic far out
of