GREAT EXTENT OF THE YALLET3. 3G5 



Rio Negro (lat. 38-39) groups of mountains seem to rise 

 in the form of islands, in the middle of a muriatiferous plain. 

 A tribe of Indians of the south (Tehuellet), have there long 

 borne the characteristic name of " men of the mountains-" 

 (Callilehet) or Serranos. From the parallel of the mouth of 

 the Bio Negro to that of Cabo Blanco (lat. 41-47), scat- 

 tered mountains on the eastern Patagonian coast denote 

 more considerable inequalities inland. All that part, how- 

 ever, of the Straits of Magellan, from the Virgins' Cape to 

 the North Cape, on the breadth of more than 30 leagues, is 

 surrounded by savannahs or Pampas ; and the Andes of 

 western Patagonia only begin to rise near the latter cape, 

 exercising a marked influence on the direction of that part of 

 the strait nearest the Pacific, proceeding from S.E. to N.W. 

 If we have given the plains or great basins of South 

 America the names of the rivers that flow in their longi- 

 tudinal furrows, we have not meant by so doing to compare 

 them to mere valleys. In the plains of the Lower Orinoco 

 and the Amazon, all the lines of the declivity doubtless reach 

 a principal recipient, and the tributaries of tributary streams, 

 that is the basins of different orders, penetrate far into the 

 group of the mountains. The upper parts or high valleys of 

 the tributary streams must be considered in a geological 

 table, as belonging to the mountainous region of the country, 

 and beyond the plains of the Lower Orinoco and the Amazon. 

 The views of the geologist are not identical with those of the 

 hydrographer. In the basin of the Rio de la Plata and Pata- 

 gonia, the waters that follow the lines of the greatest declivi- 

 ties have many issues. The same basin contains several 

 valleys of rivers ; and when we examine nearly the polyedric 

 surface of the Pampas and the portion of their waters which, 

 like the waters of the steppes of Asia, do not go to the sea, 

 we conceive that these plains are divided by small ridges or 

 lines of elevation, and have alternate slopes, inclined, with 

 reference to the horizon, in opposite directions. In order to 

 point out more clearly the difference between geological and 

 hydrographic views, and to prove that in the former, abstract- 

 ing the course of the waters which meet in one recipient, we 

 obtain a far more general point of view, I shall here again 

 recur to the hydrographic basin of the Orinoco. That im- 

 mense river rises on the southern slope of the Sierra Pariiiie 



