If This Great Bed
Of Pebbles, Without Including The Mud Necessarily Derived
From Their Attrition, Was Piled Into A Mound, It Would Form A
Great Mountain Chain!
When we consider that all these
pebbles, countless as the grains of sand in the desert, have
been derived
From the slow falling of masses of rock on the
old coast-lines and banks of rivers, and that these fragments
have been dashed into smaller pieces, and that each of them
has since been slowly rolled, rounded, and far transported
the mind is stupefied in thinking over the long, absolutely
necessary, lapse of years. Yet all this gravel has been
transported, and probably rounded, subsequently to the
deposition of the white beds, and long subsequently to the
underlying beds with the tertiary shells.
Everything in this southern continent has been effected
on a grand scale: the land, from the Rio Plata to Tierra del
Fuego, a distance of 1200 miles, has been raised in mass (and
in Patagonia to a height of between 300 and 400 feet), within
the period of the now existing sea-shells. The old and
weathered shells left on the surface of the upraised plain still
partially retain their colours. The uprising movement has
been interrupted by at least eight long periods of rest, during
which the sea ate, deeply back into the land, forming at
successive levels the long lines of cliffs, or escarpments,
which separate the different plains as they rise like steps one
behind the other. The elevatory movement, and the eating-back
power of the sea during the periods of rest, have been
equable over long lines of coast; for I was astonished to
find that the step-like plains stand at nearly corresponding
heights at far distant points. The lowest plain is 90 feet
high; and the highest, which I ascended near the coast, is
950 feet; and of this, only relics are left in the form of flat
gravel-capped hills. The upper plain of Santa Cruz slopes
up to a height of 3000 feet at the foot of the Cordillera. I
have said that within the period of existing sea-shells,
Patagonia has been upraised 300 to 400 feet: I may add, that
within the period when icebergs transported boulders over
the upper plain of Santa Cruz, the elevation has been at least
1500 feet. Nor has Patagonia been affected only by upward
movements: the extinct tertiary shells from Port St. Julian
and Santa Cruz cannot have lived, according to Professor E.
Forbes, in a greater depth of water than from 40 to 250 feet;
but they are now covered with sea-deposited strata from 800
to 1000 feet in thickness: hence the bed of the sea, on which
these shells once lived, must have sunk downwards several
hundred feet, to allow of the accumulation of the superincumbent
strata. What a history of geological changes does the
simply-constructed coast of Patagonia reveal!
At Port St. Julian, [12] in some red mud capping the gravel
on the 90-feet plain, I found half the skeleton of the
Macrauchenia Patachonica, a remarkable quadruped, full as large
as a camel.
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