It Is An Old Story, But Not The Less
Wonderful, To Hear Of Shells Which Were Once Crawling On The
Bottom Of The Sea, Now Standing Nearly 14,000 Feet Above Its
Level.
The lower beds in this great pile of strata, have been
dislocated, baked, crystallized and almost blended together,
through the agency of mountain masses of a peculiar white
soda-granitic rock.
The other main line, namely, that of the Portillo, is of a
totally different formation: it consists chiefly of grand bare
pinnacles of a red potash-granite, which low down on the
western flank are covered by a sandstone, converted by the
former heat into a quartz-rock. On the quartz, there rest
beds of a conglomerate several thousand feet in thickness,
which have been upheaved by the red granite, and dip at an
angle of 45 degs. towards the Peuquenes line. I was astonished
to find that this conglomerate was partly composed of pebbles,
derived from the rocks, with their fossil shells, of the
Peuquenes range; and partly of red potash-granite, like that
of the Portillo. Hence we must conclude, that both the Peuquenes
and Portillo ranges were partially upheaved and exposed
to wear and tear, when the conglomerate was forming;
but as the beds of the conglomerate have been thrown off at
an angle of 45 degs. by the red Portillo granite (with the
underlying sandstone baked by it), we may feel sure, that the
greater part of the injection and upheaval of the already
partially formed Portillo line, took place after the
accumulation of the conglomerate, and long after the elevation
of the Peuquenes ridge.
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