112 BAHIA BLANC A TO BUENOS AY RES chap. 



crumbling argillaceo-calcareous rock, which, from the dry nature 

 of the cHmate, supports only scattered tufts of withered grass, 

 without a single bush or tree to break the monotonous uniformity. 

 The weather was fine, but the atmosphere remarkably hazy ; I 

 thought the appearance foreboded a gale, but the Gauchos said 

 it was owing to the plain, at some great distance in the interior, 

 being on fire. After a long gallop, having changed horses 

 twice, we reached the Rio Sauce : it is a deep, rapid, little stream, 

 not above twenty-five feet wide. The second posta on the 

 road to Buenos Ayres stands on its banks ; a little above there 

 is a ford for horses, where the water does not reach to the 

 horses' belly ; but from that point, in its course to the sea, it is 

 quite impassable, and hence makes a most useful barrier against 

 the Indians. 



Insignificant as this stream is, the Jesuit Falconer, whose 

 information is generally so very correct, figures it as a consider- 

 able river, rising at the foot of the Cordillera. With respect 

 to its source, I do not doubt that this is the case ; for the 

 Gauchos assured me, that in the middle of the dry summer 

 this stream, at the same time with the Colorado, has periodical 

 floods, which can only originate in the snow melting on the 

 Andes. It is extremely improbable that a stream so small as 

 the Sauce then was should traverse the entire width of the 

 continent ; and indeed, if it were the residue of a large river, 

 its waters, as in other ascertained cases, would be saline. 

 During the winter we must look to the springs round the Sierra 

 Ventana as the source of its pure and limpid stream. I suspect 

 the plains of Patagonia, like those of Australia, are traversed 

 by many watercourses, which only perform their proper parts 

 at certain periods. Probably this is the case with the water 

 which flows into the head of Port Desire, and likewise with 

 the Rio Chupat, on the banks of which masses of highly 

 cellular scoriae were found by the officers employed in the 

 survey. 



As it was early in the afternoon when we arrived, we took 

 fresh horses and a soldier for a guide, and started for the 

 Sierra de la Ventana. This mountain is visible from the 

 anchorage at Bahia Blanca ; and Captain Fitz Roy calculates its 

 height to be 3340 feet — an altitude very remarkable on this 

 eastern side of the continent. I am not aware that any 



