Rio Plata--Flocks of butterflies--Beetles alive in the sea--Aeronaut
spiders--Pelagic animals--Phosphorescence of sea--Port Desire--Spanish
settlements--Zoology--Guanaco--Excursion to head of harbour--Indian
grave--Port St. Julian--Geology of Patagonia, successive terraces,
transport of pebbles--Fossil gigantic llama--Types of organization
constant--Change in zoology of America--Causes of extinction.
PATAGONIA.
DECEMBER 6TH, 1833.--The Beagle sailed from the Rio Plata, never
again to enter its muddy stream. Our course was directed to Port
Desire, on the coast of Patagonia. Before proceeding any further, I
will here put together a few observations made at sea.
Several times when the ship has been some miles off the mouth of the
Plata, and at other times when off the shores of Northern Patagonia,
we have been surrounded by insects. One evening, when we were about
ten miles from the Bay of San Blas, vast numbers of butterflies, in
bands or flocks of countless myriads, extended as far as the eye
could range. Even by the aid of a glass it was not possible to see
a space free from butterflies. The seamen cried out “it was snowing
butterflies,” and such in fact was the appearance. More species than
one were present, but the main part belonged to a kind very similar
to, but not identical with, the common English _Colias edusa_.[1]
Some moths and hymenoptera accompanied the butterflies; and a fine
Calosoma flew on board. Other instances are known of this beetle
having been caught far out at sea; and this is the more remarkable,
as the greater number of the Carabidæ seldom or never take wing.
The day had been fine and calm, and the one previous to it equally
so, with light and variable airs. Hence we cannot suppose that the
insects were blown off the land, but we must conclude that they
voluntarily took flight. The great bands of the Colias seem at first
to afford an instance like those on record of the migrations of
_Vanessa cardui_;[2] but the presence of other insects makes the case
distinct, and not so easily intelligible. Before sunset, a strong
breeze sprung up from the north, and this must have been the cause
of tens of thousands of the butterflies and other insects having
perished.
On another occasion, when seventeen miles off Cape Corrientes, I had
a net overboard to catch pelagic animals. Upon drawing it up, to my
surprise I found a considerable number of beetles in it, and although
in the open sea, they did not appear much injured by the salt water.
I lost some of the specimens, but those which I preserved, belonged
to the genera, colymbetes, hydroporus, hydrobius (two species),
notaphus, cynucus, adimonia, and scarabæus. At first, I thought that
these insects had been blown from the shore; but upon reflecting that
out of the eight species, four were aquatic, and two others partly
so in their habits, it appeared to me most probable that they were
floated into the sea, by a small stream which drains a lake near Cape
Corrientes. On any supposition, it is an interesting circumstance
to find insects, quite alive, swimming in the open ocean, seventeen
miles from the nearest point of land. There are several accounts of
insects having been blown off the Patagonian shore. Captain Cook
observed it, as did more lately Captain King in the Adventure. The
cause probably is due to the want of shelter, both of trees and
hills, so that an insect on the wing with an off-shore breeze, would
be very apt to be blown out to sea. The most remarkable instance I
ever knew of an insect being caught far from the land, was that of a
large grasshopper (_Acrydium_), which flew on board, when the Beagle
was to windward of the Cape de Verd Islands, and when the nearest
point of land, not directly opposed to the trade-wind, was Cape
Blanco on the coast of Africa, 370 miles distant.[3]
On several occasions, when the vessel has been within the mouth of
the Plata, the rigging has been coated with the web of the Gossamer
Spider. One day (November 1st, 1832) I paid particular attention
to the phenomenon. The weather had been fine and clear, and in the
morning the air was full of patches of the flocculent web, as on an
autumnal day in England. The ship was sixty miles distant from the
land, in the direction of a steady though light breeze. Vast numbers
of a small spider, about one-tenth of an inch in length, and of a
dusky red colour were attached to the webs. There must have been, I
should suppose, some thousands on the ship. The little spider when
first coming in contact with the rigging, was always seated on a
single thread, and not on the flocculent mass. This latter seems
merely to be produced by the entanglement of the single threads.
The spiders were all of one species, but of both sexes, together
with young ones. These latter were distinguished by their smaller
size, and more dusky colour. I will not give the description of
this spider, but merely state that it does not appear to me to be
included in any of Latreille’s genera. The little aeronaut as soon
as it arrived on board, was very active, running about; sometimes
letting itself fall, and then reascending the same thread; sometimes
employing itself in making a small and very irregular mesh in the
corners between the ropes. It could run with facility on the surface
of water. When disturbed it lifted up its front legs, in the attitude
of attention. On its first arrival it appeared very thirsty, and with
exserted maxillæ drank eagerly of the fluid; this same circumstance
has been observed by Strack: may it not be in consequence of the
little insect having passed through a dry and rarefied atmosphere?
Its stock of web seemed inexhaustible. While watching some that were
suspended by a single thread, I several times observed that the
slightest breath of air bore them away out of sight, in a horizontal
line. On another occasion (25th) under similar circumstances, I
repeatedly observed the same kind of small spider, either when
placed, or having crawled, on some little eminence, elevate its
abdomen, send forth a thread, and then sail away in a lateral course,
but with a rapidity which was quite unaccountable. I thought I could
perceive that the spider before performing the above preparatory
steps, connected its legs together with the most delicate threads,
but I am not sure, whether this observation is correct.
One day, at St. Fe, I had a better opportunity of observing some
similar facts. A spider which was about three-tenths of an inch in
length, and which in its general appearance resembled a Citigrade
(therefore quite different from the gossamer), while standing on
the summit of a post, darted forth four or five threads from its
spinners. These glittering in the sunshine, might be compared to
rays of light; they were not, however, straight, but in undulations
like a film of silk blown by the wind. They were more than a yard in
length, and diverged in an ascending direction from the orifices.
The spider then suddenly let go its hold, and was quickly borne out
of sight. The day was hot and apparently quite calm; yet under such
circumstances the atmosphere can never be so tranquil, as not to
affect a vane so delicate as the thread of a spider’s web. If during
a warm day we look either at the shadow of any object cast on a
bank, or over a level plain at a distant landmark, the effect of an
ascending current of heated air will almost always be evident. And
this probably would be sufficient to carry with it so light an object
as the little spider on its thread. The circumstance of spiders of
the same species but of different sexes and ages, being found on
several occasions at the distance of many leagues from the land,
attached in vast numbers to the lines, proves that they are the
manufacturers of the mesh, and that the habit of sailing through the
air, is probably as characteristic of some tribe, as that of diving
is of the Argyroneta. We may then reject Latreille’s supposition,
that the gossamer owes its origin to the webs of the young of several
genera, as Epeira or Thomisa: although, as we have seen that the
young of other spiders do possess the power of performing aerial
voyages.[4]
During our different passages south of the Plata, I often towed
astern a net made of bunting, and thus caught many curious
animals. The structure of the Beroe (a kind of jelly fish) is most
extraordinary, with its rows of vibratory ciliæ, and complicated
though irregular system of circulation. Of Crustacea, there were
many strange and undescribed genera. One, which in some respects is
allied to the Notopods (or those crabs which have their posterior
legs placed almost on their backs, for the purpose of adhering to the
under side of ledges), is very remarkable from the structure of its
hind pair of legs. The penultimate joint, instead of being terminated
by a simple claw, ends in three bristle-like appendages of dissimilar
lengths,--the longest equalling that of the entire leg. These claws
are very thin, and are serrated with teeth of an excessive fineness,
which are directed towards the base. The curved extremities are
flattened, and on this part five most minute cups are placed, which
seem to act in the same manner as the suckers on the arms of the
cuttle-fish. As the animal lives in the open sea, and probably wants
a place of rest, I suppose this beautiful structure is adapted to
take hold of the globular bodies of the Medusæ, and other floating
marine animals.
In deep water, far from the land, the number of living creatures is
extremely small: south of the latitude 35°, I never succeeded in
catching any thing besides some beroe, and a few species of minute
crustacea belonging to the Entomostraca. In shoaler water, at the
distance of a few miles from the coast, very many kinds of crustacea
and some other animals were numerous, but only during the night.
Between latitudes 56° and 57° south of Cape Horn the net was put
astern several times; it never, however, brought up any thing besides
a few of two extremely minute species of Entomostraca. Yet whales and
seals, petrels and albatross, are exceedingly abundant throughout
this part of the ocean. It has always been a source of mystery to
me, on what the latter, which live far from the shore, can subsist.
I presume the albatross, like the condor, is able to fast long; and
that one good feast on the carcass of a putrid whale lasts for a long
siege of hunger. It does not lessen the difficulty to say, they feed
on fish; for on what can the fish feed? It often occurred to me,
when observing how the waters of the central and intertropical parts
of the Atlantic,[5] swarmed with Pteropoda, Crustacea, and Radiata,
and with their devourers the flying-fish, and again with _their_
devourers the bonitos and albicores, that the lowest of these pelagic
animals perhaps possess the power of decomposing carbonic acid gas,
like the members of the vegetable kingdom.
While sailing in these latitudes on one very dark night, the sea
presented a wonderful and most beautiful spectacle. There was a
fresh breeze, and every part of the surface, which during the day is
seen as foam, now glowed with a pale light. The vessel drove before
her bows two billows of liquid phosphorus, and in her wake she was
followed by a milky train. As far as the eye reached, the crest
of every wave was bright, and the sky above the horizon, from the
reflected glare of these livid flames, was not so utterly obscure, as
over the rest of the heavens.
As we proceed further southward, the sea is seldom phosphorescent;
and off Cape Horn, I do not recollect more than once having seen
it so, and then it was far from being brilliant. This circumstance
probably has a close connexion with the scarcity of organic beings in
that part of the ocean. After the elaborate paper[6] by Ehrenberg,
on the phosphorescence of the sea, it is almost superfluous on my
part to make any observations on the subject. I may however add,
that the same torn and irregular particles of gelatinous matter,
described by Ehrenberg, seem in the southern as well as in the
northern hemisphere, to be the common cause of this phenomenon. The
particles were so minute as easily to pass through fine gauze; yet
many were distinctly visible by the naked eye. The water when placed
in a tumbler and agitated gave out sparks, but a small portion in
a watch-glass, scarcely ever was luminous. Ehrenberg states, that
these particles all retain a certain degree of irritability. My
observations, some of which were made directly after taking up the
water, would give a different result. I may also mention, that having
used the net during one night I allowed it to become partially dry,
and having occasion twelve hours afterwards, to employ it again, I
found the whole surface sparkled as brightly as when first taken out
of the water. It does not appear probable in this case, that the
particles could have remained so long alive. I remark also in my
notes, that having kept a Medusa of the genus Dianæa, till it was
dead, the water in which it was placed became luminous. When the
waves scintillate with bright green sparks, I believe it is generally
owing to minute crustacea. But there can be no doubt that very many
other pelagic animals, when alive, are phosphorescent.
On two occasions I have observed the sea luminous at considerable
depths beneath the surface. Near the mouth of the Plata some
circular and oval patches, from two to four yards in diameter, and
with defined outlines, shone with a steady, but pale light; while
the surrounding water only gave out a few sparks. The appearance
resembled the reflection of the moon, or some luminous body; for the
edges were sinuous from the undulation of the surface. The ship,
which drew thirteen feet water, passed over, without disturbing,
these patches. Therefore we must suppose that some animals were
congregated together at a greater depth than the bottom of the vessel.
Near Fernando Noronha the sea gave out light in flashes. The
appearance was very similar to that which might be expected from a
large fish moving rapidly through a luminous fluid. To this cause
the sailors attributed it; at the time, however, I entertained some
doubts, on account of the frequency and rapidity of the flashes. With
respect to any general observations, I have already stated that the
display is very much more common in warm than in cold countries. I
have sometimes imagined that a disturbed electrical condition of the
atmosphere was most favourable to its production. Certainly I think
the sea is most luminous after a few days of more calm weather than
ordinary, during which time it has swarmed with various animals.
Observing that the water charged with gelatinous particles is in
an impure state, and that the luminous appearance in all common
cases is produced by the agitation of the fluid in contact with
the atmosphere, I have always been inclined to consider that the
phosphorescence was the result of the decomposition of the organic
particles, by which process (one is tempted almost to call it a kind
of respiration) the ocean becomes purified.
DECEMBER 23D.--We arrived at Port Desire, situated in lat. 47°, on
the coast of Patagonia. The creek runs for about twenty miles inland,
with an irregular width. The Beagle anchored a few miles within the
entrance in front of the ruins of an old Spanish settlement.
The same evening I went on shore. The first landing in any new
country is very interesting, and especially when, as in this
case, the whole aspect bears the stamp of a marked and individual
character. At the height of between two and three hundred feet,
above some masses of porphyry, a wide plain extends, which is truly
characteristic of Patagonia. The surface is quite level, and is
composed of well-rounded shingle mixed with a whitish earth. Here
and there scattered tufts of brown wiry grass are supported, and
still more rarely some low thorny bushes. The weather is dry and
pleasant, for the fine blue sky is but seldom obscured. When standing
in the middle of one of these desert plains, the view on one side is
generally bounded by the escarpment of another plain, rather higher,
but equally level and desolate; and on the other side it becomes
indistinct from the trembling mirage which seems to rise from the
heated surface.
The plains are traversed by many broad, flat-bottomed valleys, and in
these the bushes grow rather more abundantly. The present drainage of
the country is quite insufficient to excavate such large channels. In
some of the valleys ancient stunted trees, growing in the very centre
of the dry watercourse, seem as if placed to prove how long a time
had elapsed, since any flood had passed that way. We have evidence,
from shells lying on the surface, that the plains of gravel have
been elevated within a recent epoch above the level of the sea; and
we must look to that period for the excavation of the valleys by the
slowly-retiring waters. From the dryness of the climate, a man may
walk for days together over these plains without finding a single
drop of water. Even at the base of the porphyry hills, there are
only a few small wells containing but little water, and that rather
saline and half putrid.
In such a country the fate of the Spanish settlement was soon
decided; the dryness of the climate during the greater part of the
year, and the occasional hostile attacks of the wandering Indians,
compelled the colonists to desert their half-finished buildings. The
style, however, in which they were commenced, showed the strong and
liberal hand of Spain in the old time. The end of all the attempts to
colonize this side of America south of 41°, have been miserable. At
Port Famine, the name expresses the lingering and extreme sufferings
of several hundred wretched people, of whom one alone survived to
relate their misfortunes. At St. Joseph’s bay, on the coast of
Patagonia, a small settlement was made; but during one Sunday the
Indians made an attack and massacred the whole party, excepting two
men, who were led captive many years among the wandering tribes. At
the Rio Negro I conversed with one of these men, now in extreme old
age.
The zoology of Patagonia is as limited as its Flora.[7] On the arid
plains a few black beetles (Heteromera) might be seen slowly crawling
about, and occasionally a lizard darting from side to side. Of birds
we have three carrion hawks, and in the valleys a few finches and
insect feeders. The _Ibis malanops_ (a species said to be found in
central Africa) is not uncommon on the most desert parts. In the
stomachs of these birds I found grasshoppers, cicadæ, small lizards,
and even scorpions.[8] At one time of the year they go in flocks, at
another in pairs: their cry is very loud and singular, and resembles
the neighing of the guanaco.
I will here give an account of this latter animal, which is very
common, and is the characteristic quadruped of the plains of
Patagonia. The Guanaco, which by some naturalists is considered as
the same animal with the Llama, but in its wild state, is the South
American representative of the camel of the East. In size it may be
compared to an ass, mounted on taller legs, and with a very long
neck. The guanaco abounds over the whole of the temperate parts
of South America, from the wooded islands of Tierra del Fuego,
through Patagonia, the hilly parts of La Plata, Chile, even to the
Cordillera of Peru. Although preferring an elevated site, it yields
in this respect to its near relative the Vicuna. On the plains of
Southern Patagonia, we saw them in greater numbers than in any other
part. Generally they go in small herds, from half a dozen to thirty
together; but on the banks of the St Cruz we saw one herd which must
have contained at least five hundred. On the northern shores of the
Strait of Magellan they are also very numerous.
Generally the guanacoes are wild and extremely wary. Mr. Stokes told
me, that he one day saw through a glass a herd of these beasts, which
evidently had been frightened, running away at full speed, although
their distance was so great that they could not be distinguished by
the naked eye. The sportsman frequently receives the first intimation
of their presence, by hearing, from a long distance, the peculiar
shrill neighing note of alarm. If he then looks attentively, he will
perhaps see the herd standing in a line on the side of some distant
hill. On approaching them, a few more squeals are given, and then off
they set at an apparently slow, but really quick canter, along some
narrow beaten track to a neighbouring hill. If, however, by chance he
should abruptly meet a single animal, or several together, they will
generally stand motionless, and intently gaze at him; then perhaps
move on a few yards, turn round, and look again. What is the cause
of this difference in their shiness? Do they mistake a man in the
distance for their chief enemy the puma? Or does curiosity overcome
their timidity? That they are curious is certain; for if a person
lies on the ground, and plays strange antics, such as throwing up
his feet in the air, they will almost always approach by degrees to
reconnoitre him. It was an artifice that was repeatedly practised
by our sportsmen with success, and it had moreover the advantage of
allowing several shots to be fired, which were all taken as parts of
the performance. On the mountains of Tierra del Fuego, and in other
places, I have more than once seen a guanaco, on being approached,
not only neigh and squeal, but prance and leap about in the most
ridiculous manner, apparently in defiance as a challenge. These
animals are very easily domesticated, and I have seen some thus kept
near the houses, although at large on their native plains. They are
in this state very bold, and readily attack a man, by striking him
from behind with both knees. It is asserted, that the motive for
these attacks is jealousy on account of their females. The wild
guanacoes, however, have no idea of defence; even a single dog will
secure one of these large animals, till the huntsman can come up.
In many of their habits they are like sheep in a flock. Thus when
they see men approaching in several directions on horseback, they
soon became bewildered, and know not which way to run. This greatly
facilitates the Indian method of hunting, for they are thus easily
driven to a central point, and are encompassed.
The guanacoes readily take to the water: several times at Port Valdes
they were seen swimming from island to island. Byron, in his voyage,
says he saw them drinking salt water. Some of our officers likewise
saw a herd apparently drinking the briny fluid from a salina near
Cape Blanco. I imagine in several parts of the country, if they do
not drink salt water, they drink none at all. In the middle of the
day, they frequently roll in the dust, in saucer-shaped hollows.
The males fight together; two one day passed quite close to me,
squealing and trying to bite each other; and several were shot with
their hides deeply scored. Herds sometimes appear to set out on
exploring-parties: at Bahia Blanca, where, within thirty miles of
the coast, these animals are extremely unfrequent, I one day saw
the tracks of thirty or forty, which had come in a direct line to
a muddy salt-water creek. They then must have perceived that they
were approaching the sea, for they had wheeled with the regularity
of cavalry, and had returned back in as straight a line as they had
advanced. The guanacoes have one singular habit, which is to me quite
inexplicable; namely, that on successive days they drop their dung
in the same defined heap. I saw one of these heaps which was eight
feet in diameter, and necessarily was composed of a large quantity.
Frezier remarks on this habit as common to the guanaco as well as to
the llama;[9] he says it is very useful to the Indians, who use the
dung for fuel, and are thus saved the trouble of collecting it.
The guanacoes appear to have favourite spots for dying in. On the
banks of the St. Cruz, the ground was actually white with bones, in
certain circumscribed spaces, which were generally bushy and all
near the river. On one such spot I counted between ten and twenty
heads. I particularly examined the bones; they did not appear,
as some scattered ones which I had seen, gnawed or broken, as if
dragged together by beasts of prey. The animals in most cases,
must have crawled, before dying, beneath and amongst the bushes.
Mr. Bynoe informs me that during the last voyage, he observed the
same circumstance on the banks of the Rio Gallegos. I do not at
all understand the reason of this, but I may observe, that the
wounded guanacoes at the St. Cruz, invariably walked towards the
river. At St. Jago in the Cape de Verd islands I remember having
seen in a retired ravine a corner under a cliff, where numerous
goats’ bones were collected: we at the time exclaimed, that it was
the burial-ground of all the goats in the island. I mention these
trifling circumstances, because in certain cases they might explain
the occurrence of a number of uninjured bones in a cave, or buried
under alluvial accumulations; and likewise the cause, why certain
mammalia are more commonly embedded than others in sedimentary
deposits. Any great flood of the St. Cruz., would wash down many
bones of the guanaco, but probably not a single one of the puma,
ostrich, or fox. I may also observe, that almost every kind of
waterfowl when wounded takes to the shore to die; so that the remains
of birds, from this cause alone and independently of other reasons,
would but rarely be preserved in a fossil state.
One day the yawl was sent under the command of Mr. Chaffers with
three days’ provisions to survey the upper part of the harbour. In
the morning we searched for some watering-places, mentioned in an
old Spanish chart. We found one creek, at the head of which there
was a trickling rill (the first we had seen) of brackish water. Here
the tide compelled us to wait several hours; and in the interval I
walked some miles into the interior. The plain as usual, consisted of
gravel, mingled with soil resembling chalk in appearance, but very
different from it in nature. From the softness of these materials it
was worn into many gullies. There was not a tree, and excepting the
guanaco, which stood on the hill-top a watchful sentinel over its
herd, scarcely an animal or a bird. All was stillness and desolation.
One reflected how many ages the plain had thus lasted, and how many
more it was doomed thus to continue. Yet in passing over these
scenes, without one bright object near, an ill-defined but strong
sense of pleasure is vividly excited.
In the evening we sailed a few miles further up, and then pitched
the tents for the night. By the middle of the next day, the yawl
was aground, and from the shoalness of the water could not proceed
any higher. The water being found partly fresh Mr. Chaffers took
the dingey, and went up two or three miles further, where she also
grounded, but in a fresh-water river. The water was muddy, and though
the stream was most insignificant in size, it would be difficult
to account for its source, except from the melting snow on the
Cordillera. At the spot where we bivouacked, we were surrounded by
bold cliffs and steep pinnacles of porphyry. I do not think I ever
saw a spot, which appeared more secluded from the rest of the world,
than this rocky crevice in the wide plain.
The second day after our return to the anchorage, a party of officers
and myself went to ransack an old Indian grave, which I had found on
the summit of a neighbouring hill. Two immense stones, each probably
weighing at least a couple of tons, had been placed in front of a
ledge of rock, about six feet high. At the bottom of the grave on
the hard rock, there was a layer of earth about a foot deep, which
must have been brought up from the plain below. Above it a pavement
of flat stones was placed, on which others were piled, so as to fill
up the space between the ledge and the two great blocks. To complete
the grave, the Indians had contrived to detach from the same ledge
a huge fragment, and to throw it over the pile so as to rest on the
two blocks. We undermined the grave on both sides, but could not find
any relics, or even bones. The latter probably had decayed long since
(in which case the grave must have been of extreme antiquity), for I
found in another place some smaller heaps, beneath which a very few
crumbling fragments could yet be distinguished, as having belonged to
a man. Falconer states, that where an Indian dies he is buried, but
that subsequently his bones are carefully taken up and carried, let
the distance be ever so great, to be deposited near the sea-coast.
This custom, I think, may be accounted for, by recollecting that
before the introduction of horses, these Indians must have led nearly
the same life as the Fuegians, and therefore generally resided in the
neighbourhood of the sea. The common prejudice of lying where one’s
ancestors have lain, would make the now roaming Indians bring the
less perishable part of their dead to their ancient burial-grounds.
JANUARY 9TH, 1834.--Before it was dark the Beagle anchored in the
fine spacious harbour of Port St. Julian, situated about one hundred
and ten miles to the south of Port Desire. We remained here eight
days. The country is nearly similar to that of Port Desire, but,
perhaps, rather more sterile. One day a party accompanied Captain
FitzRoy on a long walk round the head of the harbour. We were
eleven hours without tasting any water, and some of the party were
quite exhausted. From the summit of a hill (since well named Thirsty
Hill) a fine lake was spied, and two of the party proceeded with
concerted signals to show whether it was fresh water. What was our
disappointment to find a snow-white expanse of salt, crystallized
in great cubes! We attributed our extreme thirst to the dryness of
the atmosphere; but whatever the cause might be, we were exceedingly
glad late in the evening to get back to the boats. Although we
could nowhere find, during our whole visit, a single drop of fresh
water, yet some must exist; for by an odd chance I found on the
surface of the salt water, near the head of the bay, a Colymbetes
not quite dead, which in all probability had lived in some not far
distant pool. Three other kinds of insects,--a Cincindela, like
_hybrida_, Cymindis, and a Harpalus, which all live on muddy flats
occasionally overflowed by the sea, and one other beetle found dead
on the plain,--completes the list of coleoptera. A good-sized fly
(Tabanus) was extremely numerous, and tormented us by its painful
bite. The common horsefly, which is so troublesome in the shady lanes
of England, belongs to this genus. We here have the puzzle, that so
frequently occurs in the case of musquitoes; on the blood of what
animals do these insects commonly feed? The guanaco is nearly the
only warmblooded quadruped, and they are present in numbers quite
inconsiderable, compared to the multitude of flies.
The foundation of porphyry is not here present, as it was at Port
Desire, and in consequence the tertiary deposits are arranged with
greater regularity. Five successive plains of different altitudes
are very distinct. The lower one is a mere fringe nearly on a level
with the sea, but the upper one is elevated 950 feet. This latter
is represented in this neighbourhood only by a few truncate conical
hills, of exactly the same height. It was very interesting to
stand on one of these flat patches of gravel, and viewing the wide
surrounding country, to speculate on the enormous quantity of matter
which must have been removed, thus to leave these mere points, as
measures of the former table-land.
I will now give a brief sketch of the geology of the grand tertiary
formation of Patagonia, which extends from the Strait of Magellan to
the Bay of S. Antonio. In Europe, deposits of the more recent eras
have generally been accumulated in small basins or trough-shaped
hollows. In South America, however, the entire plains of Patagonia
extending seven hundred miles in length, and backed on the one hand
by the chain of the Andes, and fronted on the other by the shores of
the Atlantic, are thus constituted. Moreover the northern boundary
is merely assumed in consequence of a mineralogical change in the
strata: if organic remains were present, it probably would be found
to be only an artificial limit. Again to the northward (1300 miles
distant from the Strait of Magellan) we have the Pampas deposit,
which though very different in composition, belongs to the same epoch
with the superficial covering of the plains of Patagonia.
The cliffs on the coast give the following section: The lower part
consists of a soft sandstone, containing large concretions of a
harder nature. These strata contain many organic remains--immense
oysters nearly a foot in diameter, curious pectens, echini,
turritellæ, and other shells, of which the greater portion are
extinct, but a few resemble those now existing on the coast.[10]
Above these fossiliferous beds, a mass of soft friable stone or earth
is superimposed, which, from its extreme whiteness, has been mistaken
for chalk. It is, however, quite different; and closely resembles the
less argillaceous varieties of decomposed felspar. This substance
never contains organic remains. Lastly, the cliff is surmounted by
a thick bed of gravel, almost exclusively derived from porphyritic
rocks. For the sake of making the following description more easily
intelligible, I have subjoined an imaginary section of the plains
near the coast. It must be observed, that the width of each plain is
in nature _very much_ greater in proportion to the height, than here
represented.
[Illustration: Fossiliferous Strata]
The whole series is horizontally stratified, and I do not recollect
ever seeing any signs of violence, not even such as a fault. The
gravel covers the entire surface of the land, from the Rio Colorado
to the Strait of Magellan, a space of 800 miles, and is one chief
cause of the desert character of Patagonia. Judging from a section
across the continent at the St. Cruz river, and from some other
reasons, I believe the gravel beds gradually thickening as they
ascend, every where reach the base of the Cordillera. It is to these
mountains we must look for the parent rocks, of at least a large
portion of the well-rounded fragments. I apprehend so great an area
covered by shingle, could scarcely be pointed out in any other part
of the world.
Having said thus much of the constitution, let us look at the
external configuration of the mass. The level plains are cut off
along the whole line of coast by perpendicular cliffs, which are
necessarily of different altitudes, because any one of the successive
terraces, which, as I have already noticed, rise like steps one
above the other, may form the sea cliff. These steps are often
several miles broad; but from one point of view I have seen four very
distinct lines of escarpment abutting one over the other. Having
observed that the plains appeared to run for great distances along
the coast at the same level, I measured barometrically the elevation
of some of them, and compared these measurements, and took all those
made by the officers employed in the survey. I was astonished to
find at how great distances, even of 600 miles, plains occurred that
had, within a few feet of difference, the same elevation. I believe
I can distinguish seven or eight distinct terraces which occur along
the line of coast, and which include heights between 1200 feet and
the level of the sea. It will be understood that they are not always
present, for the lower ones have in some parts been removed by the
action of the sea sooner than in others. When any broad valley enters
the country, the terraces sweep round and run up on each side; in
which case, the correspondence on the opposite sides is beautifully
illustrated.
I have called these step-like plains level, because they appear to be
absolutely so to the eye, but in truth they rise a little between the
edge of one line of cliff and the base of the next above it. Their
slope is about the same as that of the gradually shoaling bottom of
the neighbouring sea. The elevation of 350 feet is gained by three
steps; one of about 100 feet, the second 250, and the third 350. Over
these three plains marine remains are frequently scattered, but they
are especially abundant on the lower one. The shells are the same
as the now existing littoral species, and the muscle and turbo yet
partially retain their blue and purple colours.
We have now stated the problem, which is to be explained so as to
connect together these various phenomena. At first I could only
understand the grand covering of gravel, by the supposition of
some epoch of extreme violence, and the successive lines of cliff,
by as many great elevations, the precise action of which I could
not however follow out. Guided by the “Principles of Geology,” and
having under my view the vast changes going on in this continent,
which at the present day seems the great workshop of nature, I came
to another, and I hope more satisfactory conclusion. The importance
of any view which may explain the agency by which such vast beds of
shingle have been transported over the surface of the successive
plains, cannot be doubted. Whatever the cause may have been, it has
determined the condition of this desert country, with respect to its
form, nature, and capabilities of supporting life.
There are proofs, that the whole coast has been elevated to a
considerable height within the recent period; and on the shores
of the Pacific, where successive terraces likewise occur, we know
that these changes have latterly been very gradual. There is indeed
reason for believing, that the uplifting of the ground during the
earthquakes in Chile, although only to the height of two or three
feet, has been a disturbance which may be considered as a great one,
in comparison to the series of lesser and scarcely sensible movements
which are likewise in progress. Let us then imagine the consequence
of the shoaling bed of an ocean, elevated at a perfectly equable
rate, so that the same number of feet should be converted into dry
land in each succeeding century. Every part of the surface would
then have been exposed for an equal length of time to the action
of the beach-line, and the whole in consequence equally modified.
The shoaling bed of the ocean would thus be changed into a sloping
land, with no marked line on it. If, however, there should occur a
long period of repose in the elevations, and the currents of the
sea should tend to wear away the land (as happens along this whole
coast), then there would be formed a line of cliff. Accordingly as
the repose was long, so would be the quantity of land consumed, and
the consequent height of such cliffs. Let the elevations recommence,
and another sloping bank (of shingle, or sand, or mud, according
to the nature of the successive beach-lines) must be formed, which
again will be broken by as many lines of cliff, as there shall be
periods of rest in the action of the subterranean forces. Now this is
the structure of the plains of Patagonia; and such gradual changes
harmonize well with the undisturbed strata, extending over so many
hundred miles.
I must here observe, that I am far from supposing that the entire
coast of this part of the continent has ever been lifted up, to
the height of even a foot, at any one moment of time; but, drawing
our analogies from the shores of the Pacific, that the whole may
have been insensibly rising, with every now and then a paroxysmal
or accelerated movement in certain spots. With respect to the
alternation of the periods of such continued rise and those of
quiescence, we may grant that they are probable, because such
alternation agrees with what we see in the action, not only of a
single volcano, but likewise of the disturbances affecting whole
regions of the earth. At the present day, to the north of the
parallel 44°, the subterranean forces are constantly manifesting
their power over a space of more than one thousand miles. But to the
southward of that line, as far as Cape Horn, an earthquake is seldom
or never experienced, and there is not a single point of eruption;
yet in former ages, as we shall hereafter show, deluges of lava
flowed from that very part. It is in conformity with our hypothesis
that this southern region of repose, is at present suffering from the
inroads of the ocean, as attested by the long line of cliff on the
Patagonian coast. Such we believe to have been the causes of this
singular configuration of the land. Nevertheless, we confess that it
at first appears startling, that the most marked intervals between
the heights of the successive plains should, instead of some great
and sudden action of the subterranean forces, only indicate a longer
period of repose.
In explaining the widely-spread bed of gravel, we must first suppose
a great mass of shingle to be collected by the action of innumerable
torrents, and the swell of an open ocean, at the submarine basis of
the Andes, prior to the elevation of the plains of Patagonia. If
such a mass should then be lifted up, and left exposed during one of
the periods of subterranean repose; a certain breadth, for instance
a mile, would be washed down, and spread out over the bottom of the
invading waters. (That the sea near the coast can carry out pebbles,
we may feel sure from the circumstance of their gradual decrease in
size, according to the distance from the coast-line.)
If this part of the sea should now be elevated, we should have a bed
of gravel, but it would be of less thickness than in the first mass,
both because it is spread over a larger area, and because it has been
much reduced by attrition. This process being repeated, we might
carry beds of gravel, always decreasing in thickness (as happens
in Patagonia) to a considerable distance from the line of parent
rock.[11] For instance, on the banks of the St. Cruz at the distance
of one hundred miles above the mouth of the river, the bed of gravel
is 212 feet thick, whereas, near the coast, it seldom exceeds 25 or
30 feet; the thickness being thus reduced to nearly one-eighth.
I have already stated that the gravel is separated from the
fossiliferous strata by some white beds of a friable substance,
singularly resembling chalk, but which cannot be compared, as far as
I am aware, with any formation in Europe. With respect to its origin,
I may observe that the well-rounded pebbles all consist of various
felspathic porphyries; and that, from their prolonged attrition,
during the successive remodellings of the whole mass, much sediment
must have been produced. I have already remarked that the white
earthy matter more closely resembles decomposed felspar, than any
other substance. If such is its origin, it would always, from its
lightness, be carried further to seaward than the pebbles. But as the
land was elevated, the beds would be brought nearer the coast-line,
and so become covered by the fresh masses of gravel which were
travelling outwards. When these white beds were themselves elevated,
they would hold a position intermediate between the gravel and the
common foundation, or the fossiliferous strata. To explain my meaning
more clearly, let us suppose the bottom of the present sea covered
to a certain distance from the coast-line, with pebbles gradually
decreasing in size, and beyond it by the white sediment. Let the
land rise, so that the beach-line, by the fall of the water, may be
carried outwards; then likewise the gravel, by the same agency as
before, will be transported so much further from the coast, and will
cover the white sediment, and these beds again will invade the more
distant parts of the bottom of the sea. By this outward progress, the
order of superposition must always be gravel, white sediment, and the
fossiliferous strata.
Such is the history of the changes by which the present condition of
Patagonia has, I believe, been determined. These changes all result
from the assumption of a steady but very gradual elevation, extending
over a wide area, and interrupted at long intervals by periods of
repose. But we must now return to Port St. Julian. On the south side
of the harbour, a cliff of about ninety feet in height intersects a
plain constituted of the formations above described; and its surface
is strewed over with recent marine shells. The gravel, however,
differently from that in every other locality, is covered by a very
irregular and thin bed of a reddish loam, containing a few small
calcareous concretions. The matter somewhat resembles that of the
Pampas, and probably owes its origin either to a small stream having
formerly entered the sea at that spot, or to a mud-bank similar to
those now existing at the head of the harbour. In one spot this
earthy matter filled up a hollow, or gully, worn quite through the
gravel, and in this mass a group of large bones was embedded. The
animal to which they belonged, must have lived, as in the case at
Bahia Blanca, at a period long subsequent to the existence of the
shells now inhabiting the coast. We may feel sure of this, because
the formation of the lower terrace or plain, must necessarily have
been posterior to those above it, and on the surface of the two
higher ones, sea-shells of recent species are scattered. From the
small physical change, which the last one hundred feet elevation
of the continent could have produced, the climate, as well as the
general condition of Patagonia, probably was nearly the same, at the
time when the animal was embedded, as it now is. This conclusion is
moreover supported by the identity of the shells belonging to the
two ages. Then immediately occurred the difficulty, how could any
large quadruped have subsisted on these wretched deserts in lat. 49°
15′? I had no idea at the time, to what kind of animal these remains
belonged. The puzzle, however, was soon solved when Mr. Owen examined
them; for he considers that they formed part of an animal allied to
the guanaco or llama, but fully as large as the true camel. As all
the existing members of the family of Camelidæ are inhabitants of the
most sterile countries, so may we suppose was this extinct kind. The
structure of the cervical vertebræ, the transverse processes not
being perforated for the vertebral artery, indicates its affinity:
some other parts, however, of its structure, probably are anomalous.
The most important result of this discovery, is the confirmation of
the law that existing animals have a close relation in form with
extinct species. As the guanaco is the characteristic quadruped of
Patagonia, and the vicuna of the snow-clad summits of the Cordillera,
so in bygone days, this gigantic species of the same family must have
been conspicuous on the southern plains. We see this same relation of
type between the existing and fossil Ctenomys, between the capybara
(but less plainly, as shown by Mr. Owen) and the gigantic Toxodon;
and lastly, between the living and extinct Edentata. At the present
day, in South America, there exist probably nineteen species of this
order, distributed into several genera; while throughout the rest of
the world there are but five. If, then, there is a relation between
the living and the dead, we should expect that the Edentata would be
numerous in the fossil state. I need only reply by enumerating the
megatherium, and the three or four other great species, discovered at
Bahia Blanca; the remains of some of which are also abundant over the
whole immense territory of La Plata. I have already pointed out the
singular relation between the armadilloes and their great prototypes,
even in a point apparently of so little importance as their external
covering.
The order of rodents at the present day, is most conspicuous in
South America, on account of the vast number[12] and size of the
species, and the multitude of individuals: according to the same law,
we should expect to find their representatives in a fossil state.
Mr. Owen has shown how far the Toxodon is thus related; and it is
moreover not improbable that another large animal has likewise a
similar affinity.
The teeth of the rodent nearly equalling in size those of the
Capybara, which were discovered near Bahia Blanca, must also be
remembered.
The law of the succession of types, although subject to some
remarkable exceptions, must possess the highest interest to every
philosophical naturalist, and was first clearly observed in regard
to Australia, where fossil remains of a large and extinct species
of Kangaroo and other marsupial animals were discovered buried in a
cave. In America the most marked change among the mammalia has been
the loss of several species of Mastodon, of an elephant, and of the
horse. These Pachydermata appear formerly to have had a range over
the world, like that which deer and antelopes now hold. If Buffon had
known of these gigantic armadilloes, llamas, great rodents, and lost
pachydermata, he would have said with a greater semblance of truth,
that the creative force in America had lost its vigour, rather than
that it had never possessed such powers.
It is impossible to reflect without the deepest astonishment, on
the changed state of this continent. Formerly it must have swarmed
with great monsters, like the southern parts of Africa, but now we
find only the tapir, guanaco, armadillo, and capybara; mere pigmies
compared to the antecedent races. The greater number, if not all,
of these extinct quadrupeds lived at a very recent period; and many
of them were contemporaries of the existing molluscs. Since their
loss, no very great physical changes can have taken place in the
nature of the country. What then has exterminated so many living
creatures? In the Pampas, the great sepulchre of such remains, there
are no signs of violence, but on the contrary, of the most quiet and
scarcely sensible changes. At Bahia Blanca I endeavoured to show the
probability that the ancient Edentata, like the present species,
lived in a dry and sterile country, such as now is found in that
neighbourhood. With respect to the camel-like llama of Patagonia,
the same grounds which, before knowing more than the size of the
remains, perplexed me, by not allowing any great change of climate,
now that we can guess the habits of the animal, are strangely
confirmed. What shall we say of the death of the fossil horse?
Did those plains fail in pasture, which afterwards were overrun
by thousands and tens of thousands of the successors of the fresh
stock introduced with the Spanish colonist? In some countries, we
may believe, that a number of species subsequently introduced, by
consuming the food of the antecedent races, may have caused their
extermination; but we can scarcely credit that the armadillo has
devoured the food of the immense Megatherium, the capybara of the
Toxodon, or the guanaco of the camel-like kind. But granting that
all such changes have been small, yet we are so profoundly ignorant
concerning the physiological relations, on which the life, and even
health (as shown by epidemics) of any existing species depends, that
we argue with still less safety about either the life or death of any
extinct kind.
One is tempted to believe in such simple relations, as variation
of climate and food, or introduction of enemies, or the increased
numbers of other species, as the cause of the succession of races.
But it may be asked whether it is probable than any such cause should
have been in action during the same epoch over the whole northern
hemisphere, so as to destroy the _Elephas primigenus_, on the shores
of Spain, on the plains of Siberia, and in Northern America; and in
a like manner, the _Bos urus_, over a range of scarcely less extent?
Did such changes put a period to the life of _Mastodon angustidens_,
and of the fossil horse, both in Europe and on the Eastern slope of
the Cordillera in Southern America? If they did, they must have been
changes common to the whole world; such as gradual refrigeration,
whether from modifications of physical geography, or from central
cooling. But on this assumption, we have to struggle with the
difficulty that these supposed changes, although scarcely sufficient
to affect molluscous animals either in Europe or South America, yet
destroyed many quadrupeds in regions now characterized by _frigid_,
_temperate_, and _warm_[13] climates! These cases of extinction
forcibly recall the idea (I do not wish to draw any close analogy)
of certain fruit-trees, which, it has been asserted, though grafted
on young stems, planted in varied situations, and fertilized by
the richest manures, yet at one period, have all withered away and
perished. A fixed and determined length of life has in such cases
been given to thousands and thousands of buds (or individual germs),
although produced in long succession. Among the greater number of
animals, each individual appears nearly independent of its kind; yet
all of one kind may be bound together by common laws, as well as
a certain number of individual buds in the tree, or polypi in the
Zoophyte.
I will add one other remark. We see that whole series of animals,
which have been created with peculiar kinds of organization, are
confined to certain areas; and we can hardly suppose these structures
are only adaptations to peculiarities of climate or country; for
otherwise, animals belonging to a distinct type, and introduced by
man, would not succeed so admirably, even to the extermination of the
aborigines. On such grounds it does not seem a necessary conclusion,
that the extinction of species, more than their creation, should
exclusively depend on the nature (altered by physical changes) of
their country. All that at present can be said with certainty, is
that, as with the individual, so with the species, the hour of life
has run its course, and is spent.
FOOTNOTES:
[1] I am indebted to Mr. Waterhouse for naming these and other
insects.
[2] Lyell’s Geology, vol. iii., p. 63.
[3] The flies which frequently accompany a ship for some days on its
passage from harbour to harbour, wandering from the vessel, are soon
lost, and all disappear.
[4] I was not at the time aware of M. Virey’s very curious
observations, (Bulletin des Sciences Natur., tom. xix., p. 130)
which seem to prove that small spiders, in an atmosphere perfectly
tranquil, and without the aid of any web, have the power of darting
through the air. M. Virey, believes that by means of a rapid
vibration of their feet, they _walk the air_. Although in his case,
the conclusion seems almost inevitable, yet in the one I have
described, we must suppose that the several threads which were sent
forth, served as sails for the atmospheric currents to act on. After
reading M. Virey’s account, it appears to me far from improbable,
that the little aeronaut actually did unite, as was suspected, its
feet together by some fine lines; thus forming artificial wings. I
regret I did not determine this point with accuracy; for it would be
a curious fact, that a spider should thus be able to take flight by
the aid of temporary wings.
[5] From my experience, which has been but little, I should say that
the Atlantic was far more prolific than the Pacific, at least, than
in that immense open area, between the west coast of America and the
extreme eastern isles of Polynesia.
[6] An abstract is given in No. IV. of the Magazine of Zoology and
Botany.
[7] I found here a species of cactus, described by Professor Henslow
under the name of _Opuntia Darwinii_ (Magazine of Zoology and Botany,
vol. i., p. 466), which was remarkable by the irritability manifested
by the stamens, when I inserted in the flower either a piece of
stick, or the end of my finger. The segments of the periant also
closed on the pistil, but more slowly than the stamens.
[8] These insects were not uncommon beneath stones. I found one
cannibal scorpion quietly devouring another.
[9] D’Orbigny says (vol. ii., p. 69) that all the species of the
genus have this habit.
[10] The geologist must recollect this is a mere sketch, and that the
fossil shells have not yet been carefully examined.
[11] It is needless to point out to the geologist, that this view, if
correct, will account, without the necessity of any sudden rush of
water, for the general covering of mixed shingle, so common in many
parts of Europe, and likewise for the occurrence of widely-extended
strata of conglomerate; for the superficial beds might, during a
period of subsidence, be covered by fresh deposits.
[12] In my collection Mr. Waterhouse distinguishes twenty-seven
species of mice; to these must be added about thirteen more, known
from the works of Azara, and other naturalists; so that we have forty
species, which have actually been described as coming from between
the Tropic and Cape Horn.
[13] The _Elephas primigenus_ is thus circumstanced, having been
found in Yorkshire (associated with recent shells: Lyell, vol. i.,
chap, vi.), in Siberia, and in the warm regions of lat. 31°, in North
America. The remains of the Mastodon occur in Paraguay (and I believe
in Brazil, in lat. 12°), as well as in the temperate plains south of
the Plata.