THE VOYAGE OF THE BEAGLE 119 



Insignificant as this stream is, the Jesuit Falconer, whose 

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

 siderable 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 water-courses, 

 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 scoria? 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 Capt. Fitz Roy cal- 

 culates its height to be 3340 feet an altitude very remark- 

 able on this eastern side of the continent. I am not aware 

 that any foreigner, previous to my visit, had ascended this 

 mountain; and indeed very few of the soldiers at Bahia 

 Blanca knew anything about it. Hence we heard of beds 

 of coal, of gold and silver, of caves, and of forests, all of 

 which inflamed my curiosity, only to disappoint it. The 

 distance from the posta was about six leagues, over a level 

 plain of the same character as before. The ride was, how- 

 ever, interesting, as the mountain began to show its true 

 form. When we reached the foot of the main ridge, we had 

 much difficulty in finding any water, and we thought we 

 should have been obliged to have passed the night without 

 any. At last we discovered some by looking close to the 

 mountain, for at the distance even of a few hundred yards, 

 the streamlets were buried and entirely lost in the friable 



