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
several competent observers, that part of an old wreck, which is firmly
embedded near the beach, has sensibly emerged; hence here, as at
Chiloe, a slow rise of the land appears to be now in progress. It seems
highly probable that the rocks which are corroded in a band at the
height of fourteen feet above the sea were acted on during the period,
when by tradition the base of S. Augustin church, now nineteen feet six
inches above the highest water-mark, was occasionally washed by the
waves.
VALPARAISO TO COQUIMBO.
For the first seventy-five miles north of Valparaiso I followed the
coast- road, and throughout this space I observed innumerable masses of
upraised shells. About Quintero there are immense accumulations (worked
for lime) of the Mesodesma donaciforme, packed in sandy earth; they
abound chiefly about fifteen feet above high-water, but shells are here
found, according to Mr. Miers, to a height of 500 feet, and at a
distance of three leagues from the coast (“Travels in Chile” volume 1
pages 395, 458. I received several similar accounts from the
inhabitants, and was assured that there are many shells on the plain of
Casa Blanca, between Valparaiso and Santiago, at the height of 800
feet.): I here noticed barnacles adhering to the rocks three or four
feet above the highest tides. In the neighbourhood of Plazilla and
Catapilco, at heights of between two hundred and three hundred feet,
the number of comminuted shells, with some perfect ones, especially of
the Mesodesma, packed in layers, was truly immense: the land at
Plazilla had evidently existed as a bay, with abrupt rocky masses
rising out of it, precisely like the islets in the broken bays now
indenting this coast. On both sides of the rivers Ligua, Longotomo,
Guachen, and Quilimari, there are plains of gravel about two hundred
feet in height, in many parts absolutely covered with shells. Close to
Conchalee, a gravel-plain is fronted by a lower and similar plain about
sixty feet in height, and this again is separated from the beach by a
wide tract of low land: the surfaces of all three plains or terraces
were strewed with vast numbers of the Concholepas, Mesodesma, an
existing Venus, and other still existing littoral shells. The two upper
terraces closely resemble in miniature the plains of Patagonia; and
like them are furrowed by dry, flat-bottomed, winding valleys.
Northward of this place I turned inward; and therefore found no more
shells: but the valleys of Chuapa, Illapel, and Limari, are bounded by
gravel-capped plains, often including a lower terrace within. These
plains send bay-like arms between and into the surrounding hills; and
they are continuously united with other extensive gravel-capped plains,
separating the coast mountain-ranges from the Cordillera.
COQUIMBO.
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