Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

1834. WATER DRAINAGE LAKE. 353 tance northward. At the place where we ceased to ascend the stream, the Santa Cruz was almost as large as at the places where we passed the first and second nights near the estuary. The velocity of the current was still at least six knots an hour though the depth remained undiminished. The temperature of the water was 45°, while that of the air was seldom so high, even in the day-time, and at night was usually below the freez- ing point. Trees, or rather the trunks of trees, were found lying upon the banks, whose water-worn appearance indicated that they had been carried far by the stream. The water was very free from sediment, though of a whitish blue colour, which induces me to suppose that it has been chiefly produced by melted snow, or that it has passed through lakes in which the sediment it might have brought so far was deposited. If filled from the waters of the nearer mountains only, its temperature would surely be lower, approaching that of melted snow : it would also, in all probability, bring much sediment, and would therefore be muddier, and less pure in colour. When one considers how large an extent of country there is between the River Negro and the Strait of Magalhaens, and that through that extensive region only one liver of magnitude flows, it may be difiicult to account for the manner in which the drainage of the eastern side of the great Cordillera is car- ried off, or where the melted snow and occasional heavy rains disappear. The Gallegos is small, though it runs into a large estuary. The Chupat river is very small : that at Port Desire is scarcely more than a brook. At times, it is true, these smaller rivers are flooded, but theit floods (added to their usual streams) seem unequal to carrying ofi" the continual drainage of the Andes. South of the Negro only the Santa Cruz flows with a full and strong stream throughout the whole year, and my idea is that the sources of the river Santa Cruz are not far from those of the southern branch of the Neerro, near the forty-fifth degree of latitude ; and that it runs at the foot of the Andes, southward, through several lakes, until it turns to the eastward in the parallel of fifty degrees. VOL. II. 2 A