Geological Observations on South AmericaDarwin, Charles
Science
Geological Observations on South America
Darwin, Charles
Beagle Expedition (1831-1836); Geology -- South America; Mollusks, Fossil -- South America; Paleontology
It is worthy of remark, that nowhere near Valparaiso above the height
of twenty feet, or rarely of fifty feet, I saw any lines of erosion on
the solid rocks, or any beds of pebbles; this, I believe, may be
accounted for by the disintegrating tendency of most of the rocks in
this neighbourhood. Nor is the land here modelled into terraces: Mr.
Alison, however, informs me, that on both sides of one narrow ravine,
at the height of 300 feet above the sea, he found a succession of
rather indistinct step-formed beaches, composed of broken shells, which
together covered a space of about eighty feet vertical.
I can add nothing to the accounts already published of the elevation of
the land at Valparaiso, which accompanied the earthquake of 1822 (Dr.
Meyen “Reise um Erde” Th. 1 s. 221, found in 1831 seaweed and other
bodies still adhering to some rocks which during the shock of 1822 were
lifted above the sea.): but I heard it confidently asserted, that a
sentinel on duty, immediately after the shock, saw a part of a fort,
which previously was not within the line of his vision, and this would
indicate that the uplifting was not horizontal: it would even appear
from some facts collected by Mr. Alison, that only the eastern half of
the bay was then elevated. Through the kindness of this same gentleman,
I am able to give an interesting account of the changes of level, which
have supervened here within historical periods: about the year 1680 a
long sea-wall (or Prefil) was built, of which only a few fragments now
remain; up to the year 1817, the sea often broke over it, and washed
the houses on the opposite side of the road (where the prison now
stands); and even in 1819, Mr. J. Martin remembers walking at the foot
of this wall, and being often obliged to climb over it to escape the
waves. There now stands (1834) on the seaward side of this wall, and
between it and the beach, in one part a single row of houses, and in
another part two rows with a street between them. This great extension
of the beach in so short a time cannot be attributed simply to the
accumulation of detritus; for a resident engineer measured for me the
height between the lowest part of the wall visible, and the present
beach-line at spring-tides, and the difference was eleven feet six
inches. The church of S. Augustin is believed to have been built in
1614, and there is a tradition that the sea formerly flowed very near
it; by levelling, its foundations were found to stand nineteen feet six
inches above the highest beach-line; so that we see in a period of 220
years, the elevation cannot have been as much as nineteen feet six
inches. From the facts given with respect to the sea-wall, and from the
testimony of the elder inhabitants, it appears certain that the change
in level began to be manifest about the year 1817. The only sudden
elevation of which there is any record occurred in 1822, and this seems
to have been less than three feet. Since that year, I was assured by
Public-domain text, read in full here on John Shaqi.
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