bulk, of Infusoria. Professor Ehrenberg has already ascertained in it
thirty oceanic forms. This bed extends for 500 miles along the coast,
and probably for a considerably greater distance. At Port St. Julian
its thickness is more than 800 feet! These white beds are everywhere
capped by a mass of gravel, forming probably one of the largest beds of
shingle in the world: it certainly extends from near the Rio Colorado
to between 600 and 700 nautical miles southward, at Santa Cruz (a river
a little south of St. Julian), it reaches to the foot of the
Cordillera; half way up the river, its thickness is more than 200 feet;
it probably everywhere extends to this great chain, whence the
well-rounded pebbles of porphyry have been derived: we may consider its
average breadth as 200 miles, and its average thickness as about 50
feet. 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
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