244 PATAGONIAN EXPEDITIONS: GEOGRAPHY. 



Pueyrredon, it flows southwesterly and is supposed to discharge its waters 

 into the Pacific by way of the northern arm of Calen Inlet. Its course 

 has never been traced and the region it traverses is one of the most moun- 

 tainous and impracticable within the entire extent of the Cordillera. 



Mayer River. This magnificent river was discovered and named by 

 the present writer during his first visit to Patagonia. It is of scarcely less 

 importance than the preceding stream. It drains Lakes Belgrano, Nansen, 

 San Martin and very likely one or more others as yet undiscovered. It 

 is also fed by numerous glaciers and, after leaving the northern arm of 

 Lake San Martin, its chief tributary, it flows almost due west and is 

 thought to enter the Pacific by way of the south fork of Calen Inlet. As 

 with the Las Heras, however, it has never been fully explored. 



Doubtless, there are many other rivers of almost equal importance to 

 those already mentioned within the extremely mountainous and almost 

 entirely unexplored region lying north of Last Hope Inlet, but as yet 

 they remain unknown and offer a certain reward to the adventurous 

 explorer who will devote his attention to this most picturesque and inter- 

 esting region. 



THE LAKES OF SOUTHERN PATAGONIA. 



The lakes of southern Patagonia may be divided according to the-ir 

 origin into three classes, viz.: residual, glacial and tectonic. Of by far the 

 greatest importance are the lakes of tectonic origin. By referring to the 

 map, an intricate series of lakes will be seen to extend in a line approx- 

 imating that of the seventy-second meridian of west longitude throughout 

 the entire length of the region under discussion. The exceedingly irreg- 

 ular outline of nearly all these bodies of water distinguishes them at once 

 as true mountain lakes. Though the eastern extremities of many of them 

 occupy lateral valleys that have been cut through the eastern range of the 

 Andes and project well out into the great plain that extends from the 

 mountains to the Atlantic, yet they one and all penetrate far to the west- 

 ward, extending quite through the eastern foothills and sending out 

 numerous arms and ramifications into that labyrinth of deep mountain 

 gorges that separates the eastern lateral range of the southern Andes from 

 the central and main range of the same mountain system. 



Many of these lakes, like Argentino, Viedma, San Martin, Pueyrredon, 

 and Buenos Aires, are of large size, fifty to one hundred miles in length, 



