subsided several thousand feet--in northern Chile as much as 6000
feet--so as to have allowed that amount of submarine strata to have
been heaped on the bed on which the shells lived. The proof is the
same with that by which it was shown, that at a much later period,
since the tertiary shells of Patagonia lived, there must have been
there a subsidence of several hundred feet, as well as an ensuing
elevation. Daily it is forced home on the mind of the geologist, that
nothing, not even the wind that blows, is so unstable as the level of
the crust of this earth.
I will make only one other geological remark: although the Portillo
chain is here higher than the Peuquenes, the waters draining the
intermediate valleys, have burst through it. The same fact, on a
grander scale, has been remarked in the eastern and loftiest line of
the Bolivian Cordillera, through which the rivers pass: analogous facts
have also been observed in other quarters of the world. On the
supposition of the subsequent and gradual elevation of the Portillo
line, this can be understood; for a chain of islets would at first
appear, and, as these were lifted up, the tides would be always wearing
deeper and broader channels between them. At the present day, even in
the most retired Sounds on the coast of Tierra del Fuego, the currents
in the transverse breaks which connect the longitudinal channels, are
very strong, so that in one transverse channel even a small vessel
under sail was whirled round and round.
About noon we began the tedious ascent of the Peuquenes ridge, and then
for the first time experienced some little difficulty in our
respiration. The mules would halt every fifty yards, and after resting
for a few seconds the poor willing animals started of their own accord
again. The short breathing from the rarefied atmosphere is called by
the Chilenos "puna;" and they have most ridiculous notions concerning
its origin. Some say "all the waters here have puna;" others that
"where there is snow there is puna;"--and this no doubt is true. The
only sensation I experienced was a slight tightness across the head and
chest, like that felt on leaving a warm room and running quickly in
frosty weather. There was some imagination even in this; for upon
finding fossil shells on the highest ridge, I entirely forgot the puna
in my delight. Certainly the exertion of walking was extremely great,
and the respiration became deep and laborious: I am told that in Potosi
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