to the mountains of that great chain for its source; and worthy of such
a source are streams that have flowed over the gently inclined bed of
the sea to a distance of one hundred miles. At the first glance of the
basaltic cliffs on the opposite sides of the valley, it was evident
that the strata once were united. What power, then, has removed along
a whole line of country, a solid mass of very hard rock, which had an
average thickness of nearly three hundred feet, and a breadth varying
from rather less than two miles to four miles? The river, though it
has so little power in transporting even inconsiderable fragments, yet
in the lapse of ages might produce by its gradual erosion an effect of
which it is difficult to judge the amount. But in this case,
independently of the insignificance of such an agency, good reasons can
be assigned for believing that this valley was formerly occupied by an
arm of the sea. It is needless in this work to detail the arguments
leading to this conclusion, derived from the form and the nature of the
step-formed terraces on both sides of the valley, from the manner in
which the bottom of the valley near the Andes expands into a great
estuary-like plain with sand-hillocks on it, and from the occurrence of
a few sea-shells lying in the bed of the river. If I had space I could
prove that South America was formerly here cut off by a strait, joining
the Atlantic and Pacific oceans, like that of Magellan. But it may yet
be asked, how has the solid basalt been moved? Geologists formerly
would have brought into play the violent action of some overwhelming
debacle; but in this case such a supposition would have been quite
inadmissible, because, the same step-like plains with existing
sea-shells lying on their surface, which front the long line of the
Patagonian coast, sweep up on each side of the valley of Santa Cruz. No
possible action of any flood could thus have modelled the land, either
within the valley or along the open coast; and by the formation of such
step-like plains or terraces the valley itself had been hollowed out.
Although we know that there are tides, which run within the Narrows of
the Strait of Magellan at the rate of eight knots an hour, yet we must
confess that it makes the head almost giddy to reflect on the number of
years, century after century, which the tides, unaided by a heavy surf,
must have required to have corroded so vast an area and thickness of
solid basaltic lava. Nevertheless, we must believe that the strata
undermined by the waters of this ancient strait, were broken up into
huge fragments, and these lying scattered on the beach were reduced
first to smaller blocks, then to pebbles and lastly to the most
impalpable mud, which the tides drifted far into the Eastern or Western
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