|
Chapter II
ON THE ELEVATION OF THE WESTERN COAST OF SOUTH AMERICA.
Chonos Archipelago.
Chiloe, recent and gradual elevation of, traditions of the inhabitants on
this subject.
Concepcion, earthquake and elevation of.
VALPARAISO, great elevation of, upraised shells, earth of marine origin,
gradual rise of the land within the historical period.
COQUIMBO, elevation of, in recent times; terraces of marine origin, their
inclination, their escarpments not horizontal.
Guasco, gravel terraces of.
Copiapo.
PERU.
Upraised shells of Cobija, Iquique, and Arica.
Lima, shell-beds and sea-beach on San Lorenzo, human remains, fossil
earthenware, earthquake debacle, recent subsidence.
On the decay of upraised shells.
General summary.
Commencing at the south and proceeding northward, the first place at which
I landed, was at Cape Tres Montes, in latitude 46 degrees 35'. Here, on the
shores of Christmas Cove, I observed in several places a beach of pebbles
with recent shells, about twenty feet above high-water mark. Southward of
Tres Montes (between latitude 47 and 48 degrees), Byron remarks, "We
thought it very strange, that upon the summits of the highest hills were
found beds of shells, a foot or two thick." ("Narrative of the Loss of the
'Wager'.") In the Chonos Archipelago, the island of Lemus (latitude 44
degrees 30') was, according to M. Coste, suddenly elevated eight feet,
during the earthquake of 1829: he adds, "Des roches jadis toujours
couvertes par la mer, restant aujourd'hui constamment decouvertes."
("Comptes Rendus" October 1838 page 706.) In other parts of this
archipelago, I observed two terraces of gravel, abutting to the foot of
each other: at Lowe's Harbour (43 degrees 48'), under a great mass of the
boulder formation, about three hundred feet in thickness, I found a layer
of sand, with numerous comminuted fragments of sea-shells, having a fresh
aspect, but too small to be identified.
THE ISLAND OF CHILOE.
The evidence of recent elevation is here more satisfactory. The bay of San
Carlos is in most parts bounded by precipitous cliffs from about ten to
forty feet in height, their bases being separated from the present line of
tidal action by a talus, a few feet in height, covered with vegetation. In
one sheltered creek (west of P. Arena), instead of a loose talus, there was
a bare sloping bank of tertiary mudstone, perforated, above the line of the
highest tides, by numerous shells of a Pholas now common in the harbour.
The upper extremities of these shells, standing upright in their holes with
grass growing out of them, were abraded about a quarter of an inch, to the
same level with the surrounding worn strata. In other parts, I observed (as
at Pudeto) a great beach, formed of comminuted shells, twenty feet above
the present shore. In other parts again, there were small caves worn into
the foot of the low cliffs, and protected from the waves by the talus with
its vegetation: one such cave, which I examined, had its mouth about twenty
feet, and its bottom, which was filled with sand containing fragments of
shells and legs of crabs, from eight to ten feet above high-water mark.
From these several facts, and from the appearance of the upraised shells, I
inferred that the elevation had been quite recent; and on inquiring from
Mr. Williams, the Portmaster, he told me he was convinced that the land had
risen, or the sea fallen, four feet within the last four years. During this
period, there had been one severe earthquake, but no particular change of
level was then observed; from the habits of the people who all keep boats
in the protected creeks, it is absolutely impossible that a rise of four
feet could have taken place suddenly and been unperceived. Mr. Williams
believes that the change has been quite gradual. Without the elevatory
movement continues at a quick rate, there can be no doubt that the sea will
soon destroy the talus of earth at the foot of the cliffs round the bay,
and will then reach its former lateral extension, but not of course its
former level: some of the inhabitants assured me that one such talus, with
a footpath on it, was even already sensibly decreasing in width.
I received several accounts of beds of shells, existing at considerable
heights in the inland parts of Chiloe; and to one of these, near Catiman, I
was guided by a countryman. Here, on the south side of the peninsula of
Lacuy, there was an immense bed of the Venus costellata and of an oyster,
lying on the summit-edge of a piece of tableland, 350 feet (by the
barometer) above the level of the sea. The shells were closely packed
together, embedded in and covered by a very black, damp, peaty mould, two
or three feet in thickness, out of which a forest of great trees was
growing. Considering the nature and dampness of this peaty soil, it is
surprising that the fine ridges on the outside of the Venus are perfectly
preserved, though all the shells have a blackened appearance. I did not
doubt that the black soil, which when dry, cakes hard, was entirely of
terrestrial origin, but on examining it under the microscope, I found many
very minute rounded fragments of shells, amongst which I could distinguish
bits of Serpulae and mussels. The Venus costellata, and the Ostrea (O.
edulis, according to Captain King) are now the commonest shells in the
adjoining bays. In a bed of shells, a few feet below the 350 feet bed, I
found a horn of the little Cervus humilis, which now inhabits Chiloe.
The eastern or inland side of Chiloe, with its many adjacent islets,
consists of tertiary and boulder deposits, worn into irregular plains
capped by gravel. Near Castro, and for ten miles southward, and on the
islet of Lemuy, I found the surface of the ground to a height of between
twenty and thirty feet above high-water mark, and in several places
apparently up to fifty feet, thickly coated by much comminuted shells,
chiefly of the Venus costellata and Mytilus Chiloensis; the species now
most abundant on this line of coast. As the inhabitants carry immense
numbers of these shells inland, the continuity of the bed at the same
height was often the only means of recognising its natural origin. Near
Castro, on each side of the creek and rivulet of the Gamboa, three distinct
terraces are seen: the lowest was estimated at about one hundred and fifty
feet in height, and the highest at about five hundred feet, with the
country irregularly rising behind it; obscure traces, also, of these same
terraces could be seen along other parts of the coast. There can be no
doubt that their three escarpments record pauses in the elevation of the
island. I may remark that several promontories have the word Huapi, which
signifies in the Indian tongue, island, appended to them, such as
Huapilinao, Huapilacuy, Caucahuapi, etc.; and these, according to Indian
traditions, once existed as islands. In the same manner the term Pulo in
Sumatra is appended to the names of promontories, traditionally said to
have been islands (Marsden's "Sumatra" page 31.); in Sumatra, as in Chiloe,
there are upraised recent shells. The Bay of Carelmapu, on the mainland
north of Chiloe, according to Aguerros, was in 1643 a good harbour
("Descripcion Hist. de la Provincia de Chiloe" page 78. From the account
given by the old Spanish writers, it would appear that several other
harbours, between this point and Concepcion, were formerly much deeper than
they now are.); it is now quite useless, except for boats.
VALDIVIA.
I did not observe here any distinct proofs of recent elevation; but in a
bed of very soft sandstone, forming a fringe-like plain, about sixty feet
in height, round the hills of mica-slate, there are shells of Mytilus,
Crepidula, Solen, Novaculina, and Cytheraea, too imperfect to be
specifically recognised. At Imperial, seventy miles north of Valdivia,
Aguerros states that there are large beds of shells, at a considerable
distance from the coast, which are burnt for lime. (Ibid page 25.) The
island of Mocha, lying a little north of Imperial, was uplifted two feet,
during the earthquake of 1835. ("Voyages of 'Adventure' and 'Beagle'"
volume 2 page 415.)
CONCEPCION.
I cannot add anything to the excellent account by Captain Fitzroy of the
elevation of the land at this place, which accompanied the earthquake of
1835. (Ibid volume 2 page 412 et seq. In volume 5 page 601 of the
"Geological Transactions" I have given an account of the remarkable
volcanic phenomena, which accompanied this earthquake. These phenomena
appear to me to prove that the action, by which large tracts of land are
uplifted, and by which volcanic eruptions are produced, is in every respect
identical.) I will only recall to the recollection of geologists, that the
southern end of the island of St. Mary was uplifted eight feet, the central
part nine, and the northern end ten feet; and the whole island more than
the surrounding districts. Great beds of mussels, patellae, and chitons
still adhering to the rocks were upraised above high-water mark; and some
acres of a rocky flat, which was formerly always covered by the sea, was
left standing dry, and exhaled an offensive smell, from the many attached
and putrefying shells. It appears from the researches of Captain Fitzroy
that both the island of St. Mary and Concepcion (which was uplifted only
four or five feet) in the course of some weeks subsided, and lost part of
their first elevation. I will only add as a lesson of caution, that round
the sandy shores of the great Bay of Concepcion, it was most difficult,
owing to the obliterating effects of the great accompanying wave, to
recognise any distinct evidence of this considerable upheaval; one spot
must be excepted, where there was a detached rock which before the
earthquake had always been covered by the sea, but afterwards was left
uncovered.
On the island of Quiriquina (in the Bay of Concepcion), I found, at an
estimated height of four hundred feet, extensive layers of shells, mostly
comminuted, but some perfectly preserved and closely packed in black
vegetable mould; they consisted of Concholepas, Fissurella, Mytilus,
Trochus, and Balanus. Some of these layers of shells rested on a thick bed
of bright-red, dry, friable earth, capping the surface of the tertiary
sandstone, and extending, as I observed whilst sailing along the coast, for
150 miles southward: at Valparaiso, we shall presently see that a similar
red earthy mass, though quite like terrestrial mould, is really in chief
part of recent marine origin. On the flanks of this island of Quiriquina,
at a less height than the 400 feet, there were spaces several feet square,
thickly strewed with fragments of similar shells. During a subsequent visit
of the "Beagle" to Concepcion, Mr. Kent, the assistant-surgeon, was so kind
as to make for me some measurements with the barometer: he found many
marine remains along the shores of the whole bay, at a height of about
twenty feet; and from the hill of Sentinella behind Talcahuano, at the
height of 160 feet, he collected numerous shells, packed together close
beneath the surface in black earth, consisting of two species of Mytilus,
two of Crepidula, one of Concholepas, of Fissurella, Venus, Mactra, Turbo,
Monoceros, and the Balanus psittacus. These shells were bleached, and
within some of the Balani other Balani were growing, showing that they must
have long lain dead in the sea. The above species I compared with living
ones from the bay, and found them identical; but having since lost the
specimens, I cannot give their names: this is of little importance, as Mr.
Broderip has examined a similar collection, made during Captain Beechey's
expedition, and ascertained that they consisted of ten recent species,
associated with fragments of Echini, crabs, and Flustrae; some of these
remains were estimated by Lieutenant Belcher to lie at the height of nearly
a thousand feet above the level of the sea. ("Zoology of Captain Beechey's
Voyage" page 162.) In some places round the bay, Mr. Kent observed that
there were beds formed exclusively of the Mytilus Chiloensis: this species
now lives in parts never uncovered by the tides. At considerable heights,
Mr. Kent found only a few shells; but from the summit of one hill, 625 feet
high, he brought me specimens of the Concholepas, Mytilus Chiloensis, and a
Turbo. These shells were softer and more brittle than those from the height
of 164 feet; and these latter had obviously a much more ancient appearance
than the same species from the height of only twenty feet.
COAST NORTH OF CONCEPCION.
The first point examined was at the mouth of the Rapel (160 miles north of
Concepcion and sixty miles south of Valparaiso), where I observed a few
shells at the height of 100 feet, and some barnacles adhering to the rocks
three or four feet above the highest tides: M. Gay found here recent shells
at the distance of two leagues from the shore. ("Annales des Scienc. Nat."
Avril 1833.) Inland there are some wide, gravel-capped plains, intersected
by many broad, flat-bottomed valleys (now carrying insignificant
streamlets), with their sides cut into successive wall-like escarpments,
rising one above another, and in many places, according to M. Gay, worn
into caves. The one cave (C. del Obispo) which I examined, resembled those
formed on many sea-coasts, with its bottom filled with shingle. These
inland plains, instead of sloping towards the coast, are inclined in an
opposite direction towards the Cordillera, like the successively rising
terraces on the inland or eastern side of Chiloe: some points of granite,
which project through the plains near the coast, no doubt once formed a
chain of outlying islands, on the inland shores of which the plains were
accumulated. At Bucalemu, a few miles northward of the Rapel, I observed at
the foot, and on the summit-edge of a plain, ten miles from the coast, many
recent shells, mostly comminuted, but some perfect. There were, also, many
at the bottom of the great valley of the Maypu. At San Antonio, shells are
said to be collected and burnt for lime. At the bottom of a great ravine
(Quebrada Onda, on the road to Casa Blanca), at the distance of several
miles from the coast, I noticed a considerable bed, composed exclusively of
Mesodesma donaciforme, Desh., lying on a bed of muddy sand: this shell now
lives associated together in great numbers, on tidal-flats on the coast of
Chile.
VALPARAISO.
During two successive years I carefully examined, part of the time in
company with Mr. Alison, into all the facts connected with the recent
elevation of this neighbourhood. In very many parts a beach of broken
shells, about fourteen or fifteen feet above high-water mark, may be
observed; and at this level the coast-rocks, where precipitous, are
corroded in a band. At one spot, Mr. Alison, by removing some birds' dung,
found at this same level barnacles adhering to the rocks. For several miles
southward of the bay, almost every flat little headland, between the
heights of 60 and 230 feet (measured by the barometer), is smoothly coated
by a thick mass of comminuted shells, of the same species, and apparently
in the same proportional numbers with those existing in the adjoining sea.
The Concholepas is much the most abundant, and the best preserved shell;
but I extracted perfectly preserved specimens of the Fissurella biradiata,
a Trochus and Balanus (both well-known, but according to Mr. Sowerby yet
unnamed) and parts of the Mytilus Chiloensis. Most of these shells, as well
as an encrusting Nullipora, partially retain their colour; but they are
brittle, and often stained red from the underlying brecciated mass of
primary rocks; some are packed together, either in black or reddish moulds;
some lie loose on the bare rocky surfaces. The total number of these shells
is immense; they are less numerous, though still far from rare, up a height
of 1,000 feet above the sea. On the summit of a hill, measured 557 feet,
there was a small horizontal band of comminuted shells, of which MANY
consisted (and likewise from lesser heights) of very young and small
specimens of the still living Concholepas, Trochus, Patellae, Crepidulae,
and of Mytilus Magellanicus (?) (Mr. Cuming informs me that he does not
think this species identical with, though closely resembling, the true M.
Magellanicus of the southern and eastern coast of South America; it lives
abundantly on the coast of Chile.): several of these shells were under a
quarter of an inch in their greatest diameter. My attention was called to
this circumstance by a native fisherman, whom I took to look at these
shell-beds; and he ridiculed the notion of such small shells having been
brought up for food; nor could some of the species have adhered when alive
to other larger shells. On another hill, some miles distant, and 648 feet
high, I found shells of the Concholepas and Trochus, perfect, though very
old, with fragments of Mytilus Chiloensis, all embedded in reddish-brown
mould: I also found these same species, with fragments of an Echinus and of
Balanus psittacus, on a hill 1,000 feet high. Above this height, shells
became very rare, though on a hill 1,300 feet high (Measured by the
barometer: the highest point in the range behind Valparaiso I found to be
1,626 feet above the level of the sea.), I collected the Concholepas,
Trochus, Fissurella, and a Patella. At these greater heights the shells are
almost invariably embedded in mould, and sometimes are exposed only by
tearing up bushes. These shells obviously had a very much more ancient
appearance than those from the lesser heights; the apices of the Trochi
were often worn down; the little holes made by burrowing animals were
greatly enlarged; and the Concholepas was often perforated quite through,
owing to the inner plates of shell having scaled off.
Many of these shells, as I have said, were packed in, and were quite filled
with, blackish or reddish-brown earth, resting on the granitic detritus. I
did not doubt until lately that this mould was of purely terrestrial
origin, when with a microscope examining some of it from the inside of a
Concholepas from the height of about one hundred feet, I found that it was
in considerable part composed of minute fragments of the spines, mouth-
bones, and shells of Echini, and of minute fragments, of chiefly very young
Patellae, Mytili, and other species. I found similar microscopical
fragments in earth filling up the central orifices of some large
Fissurellae. This earth when crushed emits a sickly smell, precisely like
that from garden-mould mixed with guano. The earth accidentally preserved
within the shells, from the greater heights, has the same general
appearance, but it is a little redder; it emits the same smell when rubbed,
but I was unable to detect with certainty any marine remains in it. This
earth resembles in general appearance, as before remarked, that capping the
rocks of Quiriquina in the Bay of Concepcion, on which beds of sea-shells
lay. I have, also, shown that the black, peaty soil, in which the shells at
the height of 350 feet at Chiloe were packed, contained many minute
fragments of marine animals. These facts appear to me interesting, as they
show that soils, which would naturally be considered of purely terrestrial
nature, may owe their origin in chief part to the sea.
Being well aware from what I have seen at Chiloe and in Tierra del Fuego,
that vast quantities of shells are carried, during successive ages, far
inland, where the inhabitants chiefly subsist on these productions, I am
bound to state that at greater heights than 557 feet, where the number of
very young and small shells proved that they had not been carried up for
food, the only evidence of the shells having been naturally left by the
sea, consists in their invariable and uniform appearance of extreme
antiquity--in the distance of some of the places from the coast, in others
being inaccessible from the nearest part of the beach, and in the absence
of fresh water for men to drink--in the shells NOT LYING IN HEAPS,--and,
lastly, in the close similarity of the soil in which they are embedded, to
that which lower down can be unequivocally shown to be in great part formed
from the debris of the sea animals. (In the "Proceedings of the Geological
Society" volume 2 page 446, I have given a brief account of the upraised
shells on the coast of Chile, and have there stated that the proofs of
elevation are not satisfactory above the height of 230 feet. I had at that
time unfortunately overlooked a separate page written during my second
visit to Valparaiso, describing the shells now in my possession from the
557 feet hill; I had not then unpacked my collections, and had not
reconsidered the obvious appearance of greater antiquity of the shells from
the greater heights, nor had I at that time discovered the marine origin of
the earth in which many of the shells are packed. Considering these facts,
I do not now feel a shadow of doubt that the shells, at the height of 1,300
feet, have been upraised by natural causes into their present position.)
With respect to the position in which the shells lie, I was repeatedly
struck here, at Concepcion, and at other places, with the frequency of
their occurrence on the summits and edges either of separate hills, or of
little flat headlands often terminating precipitously over the sea. The
several above-enumerated species of mollusca, which are found strewed on
the surface of the land from a few feet above the level of the sea up to
the height of 1,300 feet, all now live either on the beach, or at only a
few fathoms' depth: Mr. Edmondston, in a letter to Professor E. Forbes,
states that in dredging in the Bay of Valparaiso, he found the common
species of Concholepas, Fissurella, Trochus, Monoceros, Chitons, etc.,
living in abundance from the beach to a depth of seven fathoms; and dead
shells occurred only a few fathoms deeper. The common Turritella cingulata
was dredged up living at even from ten to fifteen fathoms; but this is a
species which I did not find here amongst the upraised shells. Considering
this fact of the species being all littoral or sub-littoral, considering
their occurrence at various heights, their vast numbers, and their
generally comminuted state, there can be little doubt that they were left
on successive beach-lines during a gradual elevation of the land. The
presence, however, of so many whole and perfectly preserved shells appears
at first a difficulty on this view, considering that the coast is exposed
to the full force of an open ocean: but we may suppose, either that these
shells were thrown during gales on flat ledges of rock just above the level
of high-water mark, and that during the elevation of the land they are
never again touched by the waves, or, that during earthquakes, such as
those of 1822, 1835, and 1837, rocky reefs covered with marine-animals were
it one blow uplifted above the future reach of the sea. This latter
explanation is, perhaps, the most probable one with respect to the beds at
Concepcion entirely composed of the Mytilus Chiloensis, a species which
lives below the lowest tides; and likewise with respect to the great beds
occurring both north and south of Valparaiso, of the Mesodesma
donaciforme,--a shell which, as I am informed by Mr. Cuming, inhabits
sandbanks at the level of the lowest tides. But even in the case of shells
having the habits of this Mytilus and Mesodesma, beds of them, wherever the
sea gently throws up sand or mud, and thus protects its own accumulations,
might be upraised by the slowest movement, and yet remain undisturbed by
the waves of each new beach-line.
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 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.
A narrow fringe-like plain, gently inclined towards the sea, here extends
for eleven miles along the coast, with arms stretching up between the
coast-mountains, and likewise up the valley of Coquimbo: at its southern
extremity it is directly connected with the plain of Limari, out of which
hills abruptly rise like islets, and other hills project like headlands on
a coast. The surface of the fringe-like plain appears level, but differs
insensibly in height, and greatly in composition, in different parts.
At the mouth of the valley of Coquimbo, the surface consists wholly of
gravel, and stands from 300 to 350 feet above the level of the sea, being
about one hundred feet higher than in other parts. In these other and lower
parts the superficial beds consist of calcareous matter, and rest on
ancient tertiary deposits hereafter to be described. The uppermost
calcareous layer is cream-coloured, compact, smooth-fractured, sub-
stalactiform, and contains some sand, earthy matter, and recent shells. It
lies on, and sends wedge-like veins into, a much more friable, calcareous,
tuff-like variety; and both rest on a mass about twenty feet in thickness,
formed of fragments of recent shells, with a few whole ones, and with small
pebbles firmly cemented together. (In many respects this upper hard, and
the underlying more friable, varieties, resemble the great superficial beds
at King George's Sound in Australia, which I have described in my
"Geological Observations on Volcanic Islands." There could be little doubt
that the upper layers there have been hardened by the action of rain on the
friable, calcareous matter, and that the whole mass has originated in the
decay of minutely comminuted sea-shells and corals.) This latter rock is
called by the inhabitants losa, and is used for building: in many parts it
is divided into strata, which dip at an angle of ten degrees seaward, and
appear as if they had originally been heaped in successive layers (as may
be seen on coral-reefs) on a steep beach. This stone is remarkable from
being in parts entirely formed of empty, pellucid capsules or cells of
calcareous matter, of the size of small seeds: a series of specimens
unequivocally showed that all these capsules once contained minute rounded
fragments of shells which have since been gradually dissolved by water
percolating through the mass. (I have incidentally described this rock in
the above work on Volcanic Islands.)
The shells embedded in the calcareous beds forming the surface of this
fringe-like plain, at the height of from 200 to 250 feet above the sea,
consist of:--
1. Venus opaca.
2. Mulinia Byronensis.
3. Pecten purpuratus.
4. Mesodesma donaciforme.
5. Turritella cingulata.
6. Monoceros costatum.
7. Concholepas Peruviana.
8. Trochus (common Valparaiso species).
9. Calyptraea Byronensis.
Although these species are all recent, and are all found in the
neighbouring sea, yet I was particularly struck with the difference in the
proportional numbers of the several species, and of those now cast up on
the present beach. I found only one specimen of the Concholepas, and the
Pecten was very rare, though both these shells are now the commonest kinds,
with the exception, perhaps, of the Calyptraea radians, of which I did not
find one in the calcareous beds. I will not pretend to determine how far
this difference in the proportional numbers depends on the age of the
deposit, and how far on the difference in nature between the present sandy
beaches and the calcareous bottom, on which the embedded shells must have
lived.
(DIAGRAM 8.--SECTION OF PLAIN OF COQUIMBO.
Section through Plain B-B and Ravine A.
Surface of plain 252 feet above sea.
A. Stratified sand, with recent shells in same proportions as on the beach,
half filling up a ravine.
B. Surface of plain, with scattered shells in nearly same proportions as on
the beach.
C. Upper calcareous bed, and D. Lower calcareous sandy bed (Losa), both
with recent shells, but not in same proportions as on the beach.
E. Upper ferrugino-sandy old tertiary stratum, and F. Lower old tertiary
stratum, both with all, or nearly all, extinct shells.)
On the bare surface of the calcareous plain, or in a thin covering of sand,
there were lying, at a height from 200 to 252 feet, many recent shells,
which had a much fresher appearance than the embedded ones: fragments of
the Concholepas, and of the common Mytilus, still retaining a tinge of its
colour, were numerous, and altogether there was manifestly a closer
approach in proportional numbers to those now lying on the beach. In a mass
of stratified, slightly agglutinated sand, which in some places covers up
the lower half of the seaward escarpment of the plain, the included shells
appeared to be in exactly the same proportional numbers with those on the
beach. On one side of a steep-sided ravine, cutting through the plain
behind Herradura Bay, I observed a narrow strip of stratified sand,
containing similar shells in similar proportional numbers; a section of the
ravine is represented in Diagram 8, which serves also to show the general
composition of the plain. I mention this case of the ravine chiefly because
without the evidence of the marine shells in the sand, any one would have
supposed that it had been hollowed out by simple alluvial action.
The escarpment of the fringe-like plain, which stretches for eleven miles
along the coast, is in some parts fronted by two or three narrow, step-
formed terraces, one of which at Herradura Bay expands into a small plain.
Its surface was there formed of gravel, cemented together by calcareous
matter; and out of it I extracted the following recent shells, which are in
a more perfect condition than those from the upper plain:--
1. Calyptraea radians.
2. Turritella cingulata.
3. Oliva Peruviana.
4. Murex labiosus, var.
5. Nassa (identical with a living species).
6. Solen Dombeiana.
7. Pecten purpuratus.
8. Venus Chilensis.
9. Amphidesma rugulosum. The small irregular wrinkles of the posterior part
of this shell are rather stronger than in the recent specimens of this
species from Coquimbo. (G.B. Sowerby.)
10. Balanus (identical with living species).
On the syenitic ridge, which forms the southern boundary of Herradura Bay
and Plain, I found the Concholepas and Turritella cingulata (mostly in
fragments), at the height of 242 feet above the sea. I could not have told
that these shells had not formerly been brought up by man, if I had not
found one very small mass of them cemented together in a friable calcareous
tuff. I mention this fact more particularly, because I carefully looked, in
many apparently favourable spots, at lesser heights on the side of this
ridge, and could not find even the smallest fragment of a shell. This is
only one instance out of many, proving that the absence of sea-shells on
the surface, though in many respects inexplicable, is an argument of very
little weight in opposition to other evidence on the recent elevation of
the land. The highest point in this neighbourhood at which I found upraised
shells of existing species was on an inland calcareous plain, at the height
of 252 feet above the sea.
It would appear from Mr. Caldcleugh's researches, that a rise has taken
place here within the last century and a half ("Proceedings of the
Geological Society" volume 2 page 446.); and as no sudden change of level
has been observed during the not very severe earthquakes, which have
occasionally occurred here, the rising has probably been slow, like that
now, or quite lately, in progress at Chiloe and at Valparaiso: there are
three well-known rocks, called the Pelicans, which in 1710, according to
Feuillee, were a fleur d'eau, but now are said to stand twelve feet above
low-water mark: the spring-tides rise here only five feet. There is another
rock, now nine feet above high-water mark, which in the time of Frezier and
Feuillee rose only five or six feet out of water. Mr. Caldcleugh, I may
add, also shows (and I received similar accounts) that there has been a
considerable decrease in the soundings during the last twelve years in the
Bays of Coquimbo, Concepcion, Valparaiso, and Guasco; but as in these cases
it is nearly impossible to distinguish between the accumulation of sediment
and the upheavement of the bottom, I have not entered into any details.
VALLEY OF COQUIMBO.
(FIGURE 9. EAST AND WEST SECTION THROUGH THE TERRACES AT COQUIMBO, WHERE
THEY DEBOUCH FROM THE VALLEY, AND FRONT THE SEA.
Vertical scale 1/10 of inch to 100 feet: horizontal scale much contracted.
Height of terrace in feet from east (high) to west (low):
Terrace F. 364
Terrace E. 302
Terrace D. shown dotted, height not given.
Terrace C. 120
Terrace B. 70
Terrace A. 25 sloping down to level of sea at Town of Coquimbo.)
The narrow coast-plain sends, as before stated, an arm, or more correctly a
fringe, on both sides, but chiefly on the southern side, several miles up
the valley. These fringes are worn into steps or terraces, which present a
most remarkable appearance, and have been compared (though not very
correctly) by Captain Basil Hall, to the parallel roads of Glen Roy in
Scotland: their origin has been ably discussed by Mr. Lyell. ("Principles
of Geology" 1st edition volume 3 page 131.) The first section which I will
give (Figure 9), is not drawn across the valley, but in an east and west
line at its mouth, where the step-formed terraces debouch and present their
very gently inclined surfaces towards the Pacific.
The bottom plain (A) is about a mile in width, and rises quite insensibly
from the beach to a height of twenty-five feet at the foot of the next
plain; it is sandy, and abundantly strewed with shells.
Plain or terrace B is of small extent, and is almost concealed by the
houses of the town, as is likewise the escarpment of terrace C. On both
sides of a ravine, two miles south of the town, there are two little
terraces, one above the other, evidently corresponding with B and C; and on
them marine remains of the species already enumerated were plentiful.
Terrace E is very narrow, but quite distinct and level; a little southward
of the town there were traces of a terrace D intermediate between E and C.
Terrace F is part of the fringe-like plain, which stretches for the eleven
miles along the coast; it is here composed of shingle, and is 100 feet
higher than where composed of calcareous matter. This greater height is
obviously due to the quantity of shingle, which at some former period has
been brought down the great valley of Coquimbo.
Considering the many shells strewed over the terraces A, B, and C, and a
few miles southward on the calcareous plain, which is continuously united
with the upper step-like plain F, there cannot, I apprehend, be any doubt,
that these six terraces have been formed by the action of the sea; and that
their five escarpments mark so many periods of comparative rest in the
elevatory movement, during which the sea wore into the land. The elevation
between these periods may have been sudden and on AN AVERAGE not more than
seventy-two feet each time, or it may have been gradual and insensibly
slow. From the shells on the three lower terraces, and on the upper one,
and I may add on the three gravel-capped terraces at Conchalee, being all
littoral and sub-littoral species, and from the analogical facts given at
Valparaiso, and lastly from the evidence of a slow rising lately or still
in progress here, it appears to me far more probable that the movement has
been slow. The existence of these successive escarpments, or old cliff-
lines, is in another respect highly instructive, for they show periods of
comparative rest in the elevatory movement, and of denudation, which would
never even have been suspected from a close examination of many miles of
coast southward of Coquimbo.
(FIGURE 10. NORTH AND SOUTH SECTION ACROSS THE VALLEY OF COQUIMBO.
From north F (high) through E?, D, C, B, A (low), B?, C, D?, E, F (high).
Vertical scale 1/10 of inch to 100 feet: horizontal scale much contracted.
Terraces marked with ? do not occur on that side of the valley, and are
introduced only to make the diagram more intelligible. A river and bottom-
plain of valley C, E, and F, on the south side of valley, are respectively,
197, 377, and 420 feet above the level of the sea.
AA. The bottom of the valley, believed to be 100 feet above the sea: it is
continuously united with the lowest plain A of Figure 9.
B. This terrace higher up the valley expands considerably; seaward it is
soon lost, its escarpment being united with that of C: it is not developed
at all on the south side of the valley.
C. This terrace, like the last, is considerably expanded higher up the
valley. These two terraces apparently correspond with B and C of Figure 9.
D is not well developed in the line of this section; but seaward it expands
into a plain: it is not present on the south side of the valley; but it is
met with, as stated under the former section, a little south of the town.
E is well developed on the south side, but absent on the north side of the
valley: though not continuously united with E of Figure 9, it apparently
corresponds with it.
F. This is the surface-plain, and is continuously united with that which
stretches like a fringe along the coast. In ascending the valley it
gradually becomes narrower, and is at last, at the distance of about ten
miles from the sea, reduced to a row of flat-topped patches on the sides of
the mountains. None of the lower terraces extend so far up the valley.)
We come now to the terraces on the opposite sides of the east and west
valley of Coquimbo: the section in Figure 10 is taken in a north and south
line across the valley at a point about three miles from the sea. The
valley measured from the edges of the escarpments of the upper plain FF is
about a mile in width; but from the bases of the bounding mountains it is
from three to four miles wide. The terraces marked with an interrogative do
not exist on that side of the valley, but are introduced merely to render
the diagram more intelligible.
These five terraces are formed of shingle and sand; three of them, as
marked by Captain B. Hall (namely, B, C, and F), are much more conspicuous
than the others. From the marine remains copiously strewed at the mouth of
the valley on the lower terraces, and southward of the town on the upper
one, they are, as before remarked, undoubtedly of marine origin; but within
the valley, and this fact well deserves notice, at a distance of from only
a mile and a half to three or four miles from the sea, I could not find
even a fragment of a shell.
ON THE INCLINATION OF THE TERRACES OF COQUIMBO, AND ON THE UPPER AND BASAL
EDGES OF THEIR ESCARPMENTS NOT BEING HORIZONTAL.
The surfaces of these terraces slope in a slight degree, as shown by the
sections in Figures 9 and 10 taken conjointly, both towards the centre of
the valley, and seawards towards its mouth. This double or diagonal
inclination, which is not the same in the several terraces, is, as we shall
immediately see, of simple explanation. There are, however, some other
points which at first appear by no means obvious,--namely, first, that each
terrace, taken in its whole breadth from the summit-edge of one escarpment
to the base of that above it, and followed up the valley, is not
horizontal; nor have the several terraces, when followed up the valley, all
the same inclination; thus I found the terraces C, E, and F, measured at a
point about two miles from the mouth of the valley, stood severally between
fifty-six to seventy-seven feet higher than at the mouth. Again, if we look
to any one line of cliff or escarpment, neither its summit-edge nor its
base is horizontal. On the theory of the terraces having been formed during
a slow and equable rise of the land, with as many intervals of rest as
there are escarpments, it appears at first very surprising that horizontal
lines of some kind should not have been left on the land.
The direction of the diagonal inclination in the different terraces being
different,--in some being directed more towards the middle of the valley,
in others more towards its mouth,--naturally follows on the view of each
terrace, being an accumulation of successive beach-lines round bays, which
must have been of different forms and sizes when the land stood at
different levels: for if we look to the actual beach of a narrow creek, its
slope is directed towards the middle; whereas, in an open bay, or slight
concavity on a coast, the slope is towards the mouth, that is, almost
directly seaward; hence as a bay alters in form and size, so will the
direction of the inclination of its successive beaches become changed.
(FIGURE 11. DIAGRAM OF A BAY IN A DISTRICT WHICH HAS BEGUN SLOWLY RISING)
If it were possible to trace any one of the many beach-lines, composing
each sloping terrace, it would of course be horizontal; but the only lines
of demarcation are the summit and basal edges of the escarpments. Now the
summit-edge of one of these escarpments marks the furthest line or point to
which the sea has cut into a mass of gravel sloping seaward; and as the sea
will generally have greater power at the mouth than at the protected head
of the bay, so will the escarpment at the mouth be cut deeper into the
land, and its summit-edge be higher; consequently it will not be
horizontal. With respect to the basal or lower edges of the escarpments,
from picturing in one's mind ancient bays ENTIRELY surrounded at successive
periods by cliff-formed shores, one's first impression is that they at
least necessarily must be horizontal, if the elevation has been horizontal.
But here is a fallacy: for after the sea has, during a cessation of the
elevation, worn cliffs all round the shores of a bay, when the movement
recommences, and especially if it recommences slowly, it might well happen
that, at the exposed mouth of the bay, the waves might continue for some
time wearing into the land, whilst in the protected and upper parts
successive beach-lines might be accumulating in a sloping surface or
terrace at the foot of the cliffs which had been lately reached: hence,
supposing the whole line of escarpment to be finally uplifted above the
reach of the sea, its basal line or foot near the mouth will run at a lower
level than in the upper and protected parts of the bay; consequently this
basal line will not be horizontal. And it has already been shown that the
summit-edges of each escarpment will generally be higher near the mouth
(from the seaward sloping land being there most exposed and cut into) than
near the head of the bay; therefore the total height of the escarpments
will be greatest near the mouth; and further up the old bay or valley they
will on both sides generally thin out and die away: I have observed this
thinning out of the successive escarpment at other places besides Coquimbo;
and for a long time I was quite unable to understand its meaning. The rude
diagram in Figure 11 will perhaps render what I mean more intelligible; it
represents a bay in a district which has begun slowly rising. Before the
movement commenced, it is supposed that the waves had been enabled to eat
into the land and form cliffs, as far up, but with gradually diminishing
power, as the points AA: after the movement had commenced and gone on for a
little time, the sea is supposed still to have retained the power, at the
exposed mouth of the bay, of cutting down and into the land as it slowly
emerged; but in the upper parts of the bay it is supposed soon to have lost
this power, owing to the more protected situation and to the quantity of
detritus brought down by the river; consequently low land was there
accumulated. As this low land was formed during a slow elevatory movement,
its surface will gently slope upwards from the beach on all sides. Now, let
us imagine the bay, not to make the diagram more complicated, suddenly
converted into a valley: the basal line of the cliffs will of course be
horizontal, as far as the beach is now seen extending in the diagram; but
in the upper part of the valley, this line will be higher, the level of the
district having been raised whilst the low land was accumulating at the
foot of the inland cliffs. If, instead of the bay in the diagram being
suddenly converted into a valley, we suppose with much more probability it
to be upraised slowly, then the waves in the upper parts of the bay will
continue very gradually to fail to reach the cliffs, which are now in the
diagram represented as washed by the sea, and which, consequently, will be
left standing higher and higher above its level; whilst at the still
exposed mouth, it might well happen that the waves might be enabled to cut
deeper and deeper, both down and into the cliffs, as the land slowly rose.
The greater or lesser destroying power of the waves at the mouths of
successive bays, comparatively with this same power in their upper and
protected parts, will vary as the bays become changed in form and size, and
therefore at different levels, at their mouths and heads, more or less of
the surfaces between the escarpments (that is, the accumulated beach-lines
or terraces) will be left undestroyed: from what has gone before we can see
that, according as the elevatory movements after each cessation recommence
more or less slowly, according to the amount of detritus delivered by the
river at the heads of the successive bays, and according to the degree of
protection afforded by their altered forms, so will a greater or less
extent of terrace be accumulated in the upper part, to which there will be
no surface at a corresponding level at the mouth: hence we can perceive why
no one terrace, taken in its whole breadth and followed up the valley, is
horizontal, though each separate beach-line must have been so; and why the
inclination of the several terraces, both transversely, and longitudinally
up the valley, is not alike.
I have entered into this case in some detail, for I was long perplexed (and
others have felt the same difficulty) in understanding how, on the idea of
an equable elevation with the sea at intervals eating into the land, it
came that neither the terraces nor the upper nor lower edges of the
escarpments were horizontal. Along lines of coast, even of great lengths,
such as that of Patagonia, if they are nearly uniformly exposed, the
corroding power of the waves will be checked and conquered by the elevatory
movement, as often as it recommences, at about the same period; and hence
the terraces, or accumulated beach-lines, will commence being formed at
nearly the same levels: at each succeeding period of rest, they will, also,
be eaten into at nearly the same rate, and consequently there will be a
much closer coincidence in their levels and inclinations, than in the
terraces and escarpments formed round bays with their different parts very
differently exposed to the action of the sea. It is only where the waves
are enabled, after a long lapse of time, slowly to corrode hard rocks, or
to throw up, owing to the supply of sediment being small and to the surface
being steeply inclined, a narrow beach or mound, that we can expect, as at
Glen Roy in Scotland ("Philosophical Transactions" 1839 page 39.), a
distinct line marking an old sea-level, and which will be strictly
horizontal, if the subsequent elevatory movements have been so: for in
these cases no discernible effects will be produced, except during the long
intervening periods of rest; whereas in the case of step-formed coasts,
such as those described in this and the preceding chapter, the terraces
themselves are accumulated during the slow elevatory process, the
accumulation commencing sooner in protected than in exposed situations, and
sooner where there is copious supply of detritus than where there is
little; on the other hand, the steps or escarpments are formed during the
stationary periods, and are more deeply cut down and into the coast-land in
exposed than in protected situations;--the cutting action, moreover, being
prolonged in the most exposed parts, both during the beginning and ending,
if slow, of the upward movement.
Although in the foregoing discussion I have assumed the elevation to have
been horizontal, it may be suspected, from the considerable seaward slope
of the terraces, both up the valley of S. Cruz and up that of Coquimbo,
that the rising has been greater inland than nearer the coast. There is
reason to believe (Mr. Place in the "Quarterly Journal of Science" 1824
volume 17 page 42.), from the effects produced on the water-course of a
mill during the earthquake of 1822 in Chile, that the upheaval one mile
inland was nearly double, namely, between five and seven feet, to what it
was on the Pacific. We know, also, from the admirable researches of M.
Bravais, that in Scandinavia the ancient sea-beaches gently slope from the
interior mountain-ranges towards the coast, and that they are not parallel
one to the other ("Voyages de la Comm. du Nord" etc. also "Comptes Rendus"
October 1842.), showing that the proportional difference in the amount of
elevation on the coast and in the interior, varied at different periods.
COQUIMBO TO GUASCO.
In this distance of ninety miles, I found in almost every part marine
shells up to a height of apparently from two hundred to three hundred feet.
The desert plain near Choros is thus covered; it is bounded by the
escarpment of a higher plain, consisting of pale-coloured, earthy,
calcareous stone, like that of Coquimbo, with the same recent shells
embedded in it. In the valley of Chaneral, a similar bed occurs in which,
differently from that of Coquimbo, I observed many shells of the
Concholepas: near Guasco the same calcareous bed is likewise met with.
In the valley of Guasco, the step-formed terraces of gravel are displaced
in a more striking manner than at any other point. I followed the valley
for thirty-seven miles (as reckoned by the inhabitants) from the coast to
Ballenar; in nearly the whole of this distance, five grand terraces,
running at corresponding heights on both sides of the broad valley, are
more conspicuous than the three best-developed ones at Coquimbo. They give
to the landscape the most singular and formal aspect; and when the clouds
hung low, hiding the neighbouring mountains, the valley resembled in the
most striking manner that of Santa Cruz. The whole thickness of these
terraces or plains seems composed of gravel, rather firmly aggregated
together, with occasional parting seams of clay: the pebbles on the upper
plain are often whitewashed with an aluminous substance, as in Patagonia.
Near the coast I observed many sea-shells on the lower plains. At Freyrina
(twelve miles up the valley), there are six terraces beside the bottom-
surface of the valley: the two lower ones are here only from two hundred to
three hundred yards in width, but higher up the valley they expand into
plains; the third terrace is generally narrow; the fourth I saw only in one
place, but there it was distinct for the length of a mile; the fifth is
very broad; the sixth is the summit-plain, which expands inland into a
great basin. Not having a barometer with me, I did not ascertain the height
of these plains, but they appeared considerably higher than those at
Coquimbo. Their width varies much, sometimes being very broad, and
sometimes contracting into mere fringes of separate flat-topped
projections, and then quite disappearing: at the one spot, where the fourth
terrace was visible, the whole six terraces were cut off for a short space
by one single bold escarpment. Near Ballenar (thirty-seven miles from the
mouth of the river), the valley between the summit-edges of the highest
escarpments is several miles in width, and the five terraces on both sides
are broadly developed: the highest cannot be less than six hundred feet
above the bed of the river, which itself must, I conceive, be some hundred
feet above the sea.
A north and south section across the valley in this part is represented in
Figure 12.
(FIGURE 12. NORTH AND SOUTH SECTION ACROSS THE VALLEY OF GUASCO, AND OF A
PLAIN NORTH OF IT.
From left (north, high) to right (south, high) through plains B and A and
the River of Guasco at the Town of Ballenar.)
On the northern side of the valley the summit-plain of gravel, A, has two
escarpments, one facing the valley, and the other a great basin-like plain,
B, which stretches for several leagues northward. This narrow plain, A,
with the double escarpment, evidently once formed a spit or promontory of
gravel, projecting into and dividing two great bays, and subsequently was
worn on both sides into steep cliffs. Whether the several escarpments in
this valley were formed during the same stationary periods with those of
Coquimbo, I will not pretend to conjecture; but if so the intervening and
subsequent elevatory movements must have been here much more energetic, for
these plains certainly stand at a much higher level than do those of
Coquimbo.
COPIAPO.
From Guasco to Copiapo, I followed the road near the foot of the
Cordillera, and therefore saw no upraised remains. At the mouth, however,
of the valley of Copiapo there is a plain, estimated by Meyen ("Reise um
die Erde" th. 1 s. 372 et seq.) between fifty and seventy feet in height,
of which the upper part consists chiefly of gravel, abounding with recent
shells, chiefly of the Concholepas, Venus Dombeyi, and Calyptraea
trochiformis. A little inland, on a plain estimated by myself at nearly
three hundred feet, the upper stratum was formed of broken shells and sand
cemented by white calcareous matter, and abounding with embedded recent
shells, of which the Mulinia Byronensis and Pecten purpuratus were the most
numerous. The lower plain stretches for some miles southward, and for an
unknown distance northward, but not far up the valley; its seaward face,
according to Meyen, is worn into caves above the level of the present
beach. The valley of Copiapo is much less steeply inclined and less direct
in its course than any other valley which I saw in Chile; and its bottom
does not generally consist of gravel: there are no step-formed terraces in
it, except at one spot near the mouth of the great lateral valley of the
Despoblado where there are only two, one above the other: lower down the
valley, in one place I observed that the solid rock had been cut into the
shape of a beach, and was smoothed over with shingle.
Northward of Copiapo, in latitude 26 degrees S., the old voyager Wafer
found immense numbers of sea-shells some miles from the coast. (Burnett's
"Collection of Voyages" volume 4 page 193.) At Cobija (latitude 22 degrees
34') M. d'Orbigny observed beds of gravel and broken shells, containing ten
species of recent shells; he also found, on projecting points of porphyry,
at a height of 300 feet, shells of Concholepas, Chiton, Calyptraea,
Fissurella, and Patella, still attached to the spots on which they had
lived. M. d'Orbigny argues from this fact, that the elevation must have
been great and sudden ("Voyage, Part Geolog." page 94. M. d'Orbigny (page
98), in summing up, says: "S'il est certain (as he believes) que tous les
terrains en pente, compris entre la mer et les montagnes sont l'ancien
rivage de la mer, on doit supposer, pour l'ensemble, un exhaussement que ce
ne serait pas moindre de deux cent metres; il faudrait supposer encore que
ce soulevement n'a point ete graduel;...mais qu'il resulterait d'une seule
et meme cause fortuite," etc. Now, on this view, when the sea was forming
the beach at the foot of the mountains, many shells of Concholepas, Chiton,
Calyptraea, Fissurella, and Patella (which are known to live close to the
beach), were attached to rocks at a depth of 300 feet, and at a depth of
600 feet several of these same shells were accumulating in great numbers in
horizontal beds. From what I have myself seen in dredging, I believe this
to be improbable in the highest degree, if not impossible; and I think
everyone who has read Professor E. Forbes's excellent researches on the
subject, will without hesitation agree in this conclusion.): to me it
appears far more probable that the movement was gradual, w
< BackForward >
|
