I 12 
BAHIA BLANCA TO BUENOS AYRES 
CHAP. 
crumbling argillaceo-calcareous rock, which, from the dry nature 
of the climate, 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 
