RIVERS OF THE ANDES. 243 



from the coast, and enters the present valley of the Rio Chico a few miles 

 above Sierra Ventana. I believe that, formerly, the Rio Chico discharged 

 its waters into the Atlantic by way of the valley of the San Julian. The 

 latter valley became obstructed by a lava flow, which may still be seen, 

 and the waters of the Rio Chico were thus diverted from their former 

 course and turned into the valley of the Rio Chalia, or Sheuen, which now 

 appears as the valley of the lower Rio Chico, while the valley of the San 

 Julian became thus reduced to its present desiccated condition. 



The de Bajos, St. Dennis and Desire Rivers. — I am acquainted with 

 these streams only at their sources near the base of the Andes. I have, 

 however, visited the mouth of the latter at Port Desire. While no one 

 has ever traced the valleys of the first two throughout their entire extent, 

 enough is known of all three to demonstrate that, throughout the greater 

 part of their courses, they are destitute of running water and are charac- 

 terized by occasional small springs. It is only near the heads of these 

 valleys, along the eastern front of the Andes, that small and relatively 

 unimportant running streams are found. 



Rivers of the Andes. — With one single exception, the important An- 

 dean rivers, all have their sources in lakes that lie mainly in the eastern 

 longitudinal valley of the mountains, or in streams that rise in the eastern 

 foothills, descend into the western continuations of the transverse valleys 

 of the plains, and then turn and pass through narrow canons cut in the 

 eastern range of the Andes, thus entering the eastern longitudinal valley, 

 which they follow for a distance, until they find a passage to the Pacific by 

 way of some narrow defile through the central and main range. 



Lion River. — This river forms the exception noted above. It is the 

 short river, some thirty miles in length, by which Lake Viedma discharges 

 its waters into Lake Argentino, and it flows in a southerly direction along 

 the bottom of the eastern longitudinal valley, as do most of the other 

 Andean rivers, throughout a portion of their courses at least. But its 

 waters are finally discharged to the eastward and into the Atlantic by 

 way of the Santa Cruz, instead of turning to the westward and empty- 

 ing into the Pacific, as do the other important rivers of these mountains. 



Rio Las Heras. — This, perhaps the most important of all the Andean 

 rivers of this region, drains Lakes Buenos Aires, Soler, Pueyrredon, 

 Brown and other smaller lakes lying either wholly or in part within the 

 eastern longitudinal valley. After leaving the western extremity of Lake 



