ato_.]

[Footnote 119: Rock-salt is found on both sides of the Andes. "The
general character of the geology of these countries would rather lead to
the opinion that its origin is in some way connected with volcanic heat
at the bottom of the sea."--Darwin's _Observations_, pt. iii., p. 235.]

[Footnote 120: "The Napo (Herndon was told) is very full of sand-banks,
and twenty days from its mouth (or near the confluence of the Curaray)
the men have to get overboard and drag the canoes!"--_Report_, p. 229.]

[Footnote 121: The chief difficulty throughout the Upper Amazon is in
getting the Indians to concentrate along the bank. But honorable dealing
would accomplish this in time.]

The Napo is the largest river in the republic. From its source in the
oriental defiles of Cotopaxi and Sincholagua to its embouchure at the
Maranon, its length is not far from eight hundred miles, or about twice
that of the Susquehanna.[122] From Napo village to the mouth of the
river our barometer showed a fall of a thousand feet. At Napo the
current is six miles an hour; between Napo and Santa Rosa there are
rapids; and between Santa Rosa and the Maranon the rate is not less than
four miles an hour. At Napo the breadth is about forty yards; at Coca
the main channel is fifteen hundred feet wide; and at Camindo it is a
full Spanish mile. Below Coca the river throws out numerous canals,
which, isolating portions of the forest-clad lowlands, create numerous
picturesque islands. Around and between them the river winds, usually
making one bend in every league. The tall trees covering them are bound
together by creeping plants into a thick jungle, the home of capybaras
and the lair of the jaguar. The islands, entirely alluvial, are
periodically flooded, and undergo a constant round of decay and
renovation. Indeed, the whole river annually changes its channel, so
that navigation is somewhat difficult. The Indians, on coming to a fork,
were frequently at a loss to know which was the main channel. Then, too,
the river is full of snags and _plaias_, or low, shelving sand-banks,
rising just above the water-level--the resort of turtles during the egg
season. It was interesting to trace the bed of the river as we floated
down; on the rapid slope of the Cordilleras rushing over or rolling
along huge boulders, which farther on were rapidly reduced in size,
till, in time, boulders were broken into pebbles, pebbles turned into
sand, and sand reduced to impalpab