THE SANTA CRUZ RIVER. 241 



south. This, together with the fact that none of the tributaries of the 

 Coy penetrates the Andes, has made this river the least important, in vol- 

 ume of water as compared with drainage area, of all the streams south of 

 the Santa Cruz. 



The Santa Cruz River. This river has its source in Lake Argentino, 

 and flows almost due east from the eastern extremity of that lake, at 

 the base of the Andes, across the Patagonian plains, through a very 

 deep valley, which opens into the Atlantic at the fiftieth parallel of south 

 latitude. It is by far the largest of all the rivers of southern Patagonia. 

 Darwin, who ascended it to within thirty miles of its source, has described 

 it as a stream with a depth in the middle of seventeen feet, an average 

 breadth of three hundred yards, and a current of from four to six knots 

 an hour. Although the most important of the rivers of these plains, it 

 drains but a very limited area of the plains region. It is unique among 

 the rivers of this region in having its source in one of the largest of the 

 mountain lakes of the Andes, and actually forms the outlet for two of 

 these lakes, namely, Viedma and Argentino. This river, therefore, actu- 

 ally drains these lakes and the extensive and exceedingly mountainous 

 region, with its numerous glacial-fed streams and rivers, tributary to 

 them. To these conditions it owes the great volume of water with 

 which it is supplied, when it emerges from Lake Argentino and starts 

 eastward across the plains. Throughout its entire course it does not 

 receive a single tributary of any importance. Owing to the fact that this 

 river has its source in these lakes, which act as storage reservoirs, with a 

 capacity and superficial area comparatively large in proportion to the 

 tributary drainage area, the volume of water in the river is subject to 

 little variation, and is practically stable throughout the year. The depth 

 of the valley varies from four hundred feet, at the coast, to about three 

 thousand feet at Lake Argentino. Throughout its entire extent the valley 

 has a breadth, from crest to crest of the opposite bluffs, averaging per- 

 haps ten miles. In the bottom there are no swamps, and the noble river 

 rushes along between not very high banks, through a valley the surface 

 of which is as sterile as that of the high pampas on either side. At a 

 distance of some twenty-five miles from the coast the current of the river 

 is met by that of the tides from the Atlantic, which, at the mouth of the 

 river, have a rise and fall of twenty-eight feet Below this point the 

 river expands into a wide bay, with a width, at the mouth of the Rio 



