PLATE III.
TYPICAL RIVER VIEW BELOW THE MOUTH OF THE NEGRO RIVER
BANK OF MAIN AMAZON STREAM IN THE VICINITY OF THE MOUTH OF THE JAPURA RIVER
Wallace estimated the country to be not more than 1000 feet above sea-level. I should judge it to be considerably less, by the trend of the country to the south of it. But even here I may be mistaken, as my aneroid was useless, for undiscovered reasons, and my opinion is based simply on the force of the currents of the rivers, the number and depth of the rapids, and the distances to the main river and thence to the sea. The height above sea-level cannot be great, for the tides are felt at Obydos, more than half-way from the ocean to the mouth of the Rio Negro, and there is no abrupt rise from the Obydos levels; indeed the slope of the land is so slight that in the middle reaches of the main river during wet seasons the floods spread for twenty miles, and there is no visible current.
The Uaupes, though lighter than the majority of southern tributaries of the Negro, is what is known as a black water river, while most of the rivers flowing in on the northern bank are white water rivers. This peculiarity, which may be as marked as the difference between ink and milk, is due apparently to the variety of soil in the country drained by the rivers. The chief tributaries of the Uaupes, the Itiya and the Uniya, are both white water streams. Spruce notes that fish are scarcer in black than in white water streams,[9] and attributes it to the absence of vegetation. This may be true in part of the Negro, but it is not true, I think, of other rivers. Certainly these have some sort of fish, for I have seen them rise. One species is known to feed on a variety of laurel berry very plentiful on some of the river-banks.
The Rio Negro itself, the waters of which are dead black, is navigable for more than a third of its course to vessels of a 4 feet draught even in the dry season, and communication is possible from its upper waters with the great northern artery of the Orinoco, through the Casiquiari, the most important of the natural canals that abound throughout the Amazon regions.
The Issa, or Putumayo—the Peruvian name is perhaps better known than the Brazilian, the true geographical one—is the first tributary of importance to join the Amazon after it has entered Brazilian territory. Of its 1028 miles only 93, according to the Brazilian Year-Book, are not navigable by steamers. This exceeds the truth, for there is practically no communication with Colombia or Ecuador by this route, as the statement would imply. In the upper reaches of the Issa rock and shingle are to be found, while 300 miles down stream hardly a stone is to be seen. The water is very muddy, and the current variable as the depth. Now it will be a swirling storm-fed torrent, the turbid water burdened with a wild flotsam of forest trees and matted vegetation, cutting into the soft layers of vegetable mould that form its banks, and rise above it as much as 25 feet in places; anon it is a sluggish stream that spreads oilily nowhither, with scarce a ripple over the deep alluvial deposits of its bed. This river is at its lowest in February and March. At its juncture with the Amazon looking upstream from the main water-way, the Issa is the more imposing of the two, for its course lies wide and fully exposed, while the Amazon bends sharply, and gives the impression that it and not its affluent is the tributary stream. Robuchon calculated that its breadth there was 600 metres, the depth 8, and the current 2½ miles an hour. He states very truly that landslides often occur on the banks of these rivers, and that such destruction of the bank, together with the quick rise and fall of the streams, may so alter the appearance of any stretch as to render it quite unrecognisable, even within a few hours. Special mention is made by him of the Papunya River, that enters on the left bank of the Issa. Forty miles from the Papunya is the Parana Miri,[10] a river with very black water and a large group of islands at its mouth. Many of the islands in these rivers are not stationary, they are floating masses of soil and vegetation, torn away from the banks when the river is in spate. They may be as much as a hundred yards from bank to bank, and birds are to be found living upon them.
PLATE IV.