is the northern slope. Of the two rivers, the Paraná is much the larger, being second only to the mighty Amazon in size. It maintains an almost uniform width of three-fourths of a mile to a mile, and a depth of 50 to 70 feet for 852 miles, in a comparatively direct line from its mouth to the confluence of the Paraguay. Above this point it is not navigable except for small vessels, at certain seasons of the year; but the Paraguay, which is undoubtedly entitled to be considered the main stream, is navigable for 1,000 miles farther. The banks of the Paraná Guayaza rise only about two feet above the water, but are of firm soil. They are covered with dense forests of a glossy-leaved tree called sieba, somewhat resembling the laurel, and a thick undergrowth of rushes. The scenery retains this general character for 98 miles, where a bluff is sighted on the right or southwest bank of the river. About ten miles higher up, the river rushes with great force through the Straits of Obligado, a pass between two steep bluffs, about half the regular width of the river apart. At this point the stream is 150 feet deep. Excepting at this place, the left bank of the river is formed by an immense, low swamp, from 15 to 30 miles in width, for 253 miles from the mouth, while the right bank, for 100 miles above the straits, is formed by the high table-land of Buenos Ayres. The first cataract of the Paraná occurs about 150 miles above the confluence of the Paraguay, and it is this which renders the upper part of the river unnavigable, except for small vessels, during the floods which annually occur. About 550 miles above this cataract are the Falls of Guaira. These are not perpendicular, as Niagara, but inclined at an angle of about 50° from the horizon, with a fall of 50 feet. Above the falls, the Paraná is 4,500 yards wide, from which it suddenly contracts between granite walls 70 to 80 yards apart. Into this pass the water rushes with such tremendous fury, that clouds of spray arise and fall in perpetual rain over the neighborhood; the roar is such that no other sound can be heard, and the listener is made deaf by the thunder; even the very earth trembles, so that it has become desolate.
The Uruguay, a great river by itself, is almost insignificant in comparison. At the mouth, its channel is broad and deep, but at 200 miles above it dwindles into a torrent six feet deep, flowing through a rocky pass 145 feet wide. It is, however, subject to floods in September and October, during which it rises at the rate of three feet per day to 50 feet above the usual low-water line. At this time, the volume of the river is greatly increased by enlargement of the waterways, and a more than tenfold increase in the velocity of the current, which, at ordinary times, is about five miles per hour in the pass described.
The Paraná, on the other hand, although, as we have already seen, similarly subject to an annual overflow, displays nothing like the violent fluctuations of supply belonging to the Uruguay. M. Révy tells us that the ordinary annual rise at Rosario, 189 miles from the mouth
