is navigable for steamers up to La
Dorada, near Honda, 561 m. above its mouth, which is closed by
sand-bars to all but light-draught vessels, and for 93 m. above the
rapids at Honda, to Girardot. The river is also navigable at high
water for small steamers up to Neiva, 100 m. farther and 1535 ft.
above sea-level, beyond which point it descends precipitously from the
plateaus of southern Colombia. The Honda rapids have a fall of only 20
ft. in a distance of 2 m., but the current is swift and the channel
tortuous for a distance of 20 m., which make it impossible for the
light-draught, flat-bottomed steamers of the lower river to ascend
them. The Cauca differs much from the Magdalena, although its
principal features are the same. The latter descends 12,500 ft. before
it becomes navigable, but at 10,000 ft. below its source the Cauca
enters a long narrow valley with an average elevation of 3500 ft.,
where it is navigable for over 200 m., and then descends 2500 ft.
through a series of impetuous rapids for a distance of about 250 m.,
between Cartago and Caceres, with a break of 60 m. above Antioquia,
where smooth water permits isolated navigation. While, therefore, the
Magdalena is navigable throughout the greater part of its course, or
from Girardot to the coast, with an abrupt break of only 20 ft. at
Honda which could easily be overcome, the Cauca has only 200 m. of
navigable water in the upper valley and another 200 m. on its lower
course before it joins the Magdalena in lat. 9 deg. 30', the two being
separated by 250 m. of canyon and rapids. So difficult is the country
through which the Cauca has cut its tortuous course that the fertile
upper valley is completely isolated from the Caribbean, and has no
other practicable outlet than the overland route from Cali to
Buenaventura, on the Pacific. The upper sources of the Cauca flow
through a highly volcanic region, and are so impregnated with
sulphuric and other acids that fish cannot live in them. This is
especially true of the Rio Vinagre, which rises on the Purace volcano.
The principal tributaries are the Piendamo, Ovejas, Palo, Amaime and
Nechi, from the central Cordillera, of which the last named is the
most important, and the Jamundi and a large number of small streams
from the Western. The largest branch of the Cauca on its western side,
however, is the San Jorge, which, though rising in the Western