EIVERS OF URUGUAY. 331 



troubled waters was the general impression at once conveyed. The mighty river, 

 vexed and hindered in its progress by a long succession of step-like reefs, had 

 spread itself out over an immense area, breaking its way in lines of foam through 

 the narrow channels worn by its action, and eddying in the deeper places with a 

 force that made the water appear to be seething upwards from concealed cauldrons. 

 The great slabs of dark, slimy rock which remained uncovered in the midst, or 

 were simply trickled over by the surging flood, literally swarmed with water- 

 fowl, drawn to the spot by the fish that lay temptingly in view in the shoal water 

 all round. The entire long-billed tribe — cranes, and herons, and storks of every 

 variety — stood there in serried files, watching their chance with a terrible ear- 

 nestness, undistracted by the myriads of restless gulls which circled above them, 

 uttering their plaintive, wearisome cry."* 



Even lower down the current is obstructed by the so-called Corralitos, 

 "little corals," reefs dangerous to large vessels, and during low water there is a 

 depth of only 10 feet at the Hervidero. Farther south the river preserves the 

 picturesque aspect of its high banks, its wooded hills, abrupt windings, and 

 shifting scenery. Below Paysandu, where it is only 700 yards wide, it begins 

 to assume the aspect of a broad estuary, with low marshy banks on the west 

 (Argentine) side, terraced cliffs and hills of divers forms on the east side. 



It is evident from these contrasts that at some former epoch the Uruguay 

 .flowed through the level plain to its junction with the Parana; then at a later 

 period it gradually shifted its bed in the direction of the east, ceaselessly eating 

 away the scarps of the Clio's, and distributing the débris along its right bank. 

 Thus the Uruguay is another illustration of the phenomenon of nor7nal erosion, 

 which in accordance with the " law of Baer," causes the rivers of the southern 

 hemisphere to encroach on their left bank, whereas in the northern hemisphere 

 the tendency is to gain on their right bank. 



The basin of the Rio Negro, by far the largest of the Uruguay affluents, com- 

 prises about half of the territory of the Republic. It takes its name, not from the 

 colour of its water, but from the sharpness with which its clear, limpid stream 

 reflects every flitting shadow. After receiving the Tacuarembo and the Yi, the 

 Rio Negro flows normally north-east and south-west ; but before reaching the 

 main stream it suddenly turns south, thus enclosing with the Uruguay the long 

 peninsular tract known as the Rincon de las Gallinas, " Poultry Yard." This 

 natural enclosure served from the early days of the colonisation as a convenient 

 place for herding cattle. 



Below the Rio Negro confluence the Uruguay expands to the proportions of a 

 broad lake with scarcely perceptible current, and even at Higueritas, its narrowest 

 point, maintaining a width of considerably over a mile. Above the island of 

 Martin Garcia the Parana mingles its waters with those of the Uruguay at the 

 head of the Rio de la Plata estuary. Sooner or later this estuary must be filled 

 in by the sediment deposited on its bed by the converging streams, and then the 



* Rumbold, The Great Silver River, p. 238. 



