316 PORTILLO PASS. [cHar. xv. 
piles of debris. At the lower end or mouths of the valleys, 
they are continuously united to those Jand-locked plains (also 
formed of shingle) at the foot of the main Cordillera, which 
I have described in a former chapter as characteristic of the 
scenery- of Chile, and which were undoubtedly deposited when 
the sea penetrated Chile, as it now does the more southern 
coasts, No one fact in the geology of South America, interested 
me more than these terraces of rudely-stratified shingle. They 
precisely resemble in composition, the matter which the torrents in 
each valley would deposit, if they were checked in their course 
by any cause, such as entering a lake or arm of the sea; but the 
torrents, instead of depositing matter, are now steadily at work 
wearing away both the solid rock and these alluvial deposits, 
along the whole line of every main valley and side valley. It is 
impossible here to give the reasons, but I am convinced that the 
shingle terraces were accumulated, during the gradual elevation 
of the Cordillera, by the torrents delivering, at successive levels, 
their detritus on the beach-heads of long narrow arms of the 
sea, first high up the valleys, then lower and lower down as the 
land slowly rose. If this be so, and J cannot doubt it, the grand 
and broken chain of the Cordillera, instead of having been sud- 
denly thrown up, as was till lately the universal, and still is the 
common opinion of geologists, has been slowly upheaved in 
mass, in the same gradual manner as the coasts of the Atlantic 
and Pacific have risen within the recent period. A multitude of 
facts in the structure of the Cordillera, on this view receive a 
simple explanation. 
The rivers which flow in these valleys ought rather to be called 
mountain-torrents. Their inclination is very great, and their 
water the colour of mud. The roar which the Maypu made, as 
it rushed over the great rounded fragments, was like that of the 
sea. Amidst the din of rushing waters, the noise from the stones, 
as they rattled one over another, was most distinctly audible even 
from adistance. This rattling noise, night and day, may be 
heard along the whole course of the torrent. The sound spoke 
eloquently .to the geologist; the thousands and thousands of 
stones, which, striking against each other, made the one dull 
uniform sound, were all hurrying in one direction. It was like 
thinking on time, where the minute that now glides past is irre- 
