sight of land. The fall of the main easterly trunk of the Amazon is
about six and a half inches per mile, equivalent to a slope of 21'--the
same as that of the Nile, and one third that of the Mississippi. Below
Jaen there are thirty cataracts and rapids; at the Pongo de Manseriche,
at the altitude of 1164 feet (according to Humboldt), it bids adieu to
mountain scenery. Between Tabatinga and the ocean the average current is
three miles an hour. It diminishes toward Para, and is every where at a
minimum in the dry season; but it always has the "swing" of an ocean
current.

Though not so rapid as the Mississippi, the Amazon is deeper. There are
seven fathoms of water at Nauta (2200 miles from the Atlantic), eleven
at Tabatinga, and twenty-seven on the average below Mandaos.[156]

[Footnote 156: The assertion of the _Ency. Metropolitana_, that "its
current has great violence and rapidity, and its depth is unfathomable,"
must be received with some allowance.]

The Amazon and its branches are subject to an annual rise of great
regularity. It does not take place simultaneously over the whole river,
but there is a succession of freshets. At the foot of the Andes the rise
commences in January; at Ega it begins about the end of February.
Coinciding with this contribution from the west, the October rains on
the highlands of Bolivia and Brazil swell the southern tributaries,
whose accumulated floods reach the main stream in February; and the
latter, unable to discharge the avalanche of waters, inundates a vast
area, and even crowds up the northern tributaries. As the Madeira,
Tapajos, and Purus subside, the Negro, fed by the spring rains in Guiana
and Venezuela, presses downward till the central stream rolls back the
now sluggish affluents from the south. There is, therefore, a rhythmical
correspondence in the rise and fall of the arms of the Amazon, so that
this great fresh-water sea sways alternately north and south; while the
onward swell in the grand trunk is a progressive undulation eastward. As
the Cambridge Professor well says: "In this oceanic river the tidal
action has an annual instead of a daily ebb and flow; it obeys a larger
orb, and is ruled by the sun and not the moon." As the southern
affluents have the greatest volume, the Amazon receives its largest
accession after the sun has been in the southern hemisphere. The rise is
gradual, increasing to one foot per day. One lowland after another sinks
beneath the flood;