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the plain, complete the list of the beetles. 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 same 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 warm-blooded quadruped, and it is found in quite
inconsiderable numbers compared with the multitude of flies.

The geology of Patagonia is interesting. Differently from Europe,
where the tertiary formations appear to have accumulated in bays,
here along hundreds of miles of coast we have one great deposit,
including many tertiary shells, all apparently extinct. The most
common shell is a massive gigantic oyster, sometimes even a foot in
diameter. These beds are covered by others of a peculiar soft white
stone, including much gypsum, and resembling chalk, but really of a
pumiceous nature. It is highly remarkable, from being composed, to
at least one-tenth part of its bulk, of Infusoria: Professor
Ehrenberg has already ascertained in it thirty oceanic forms. This
bed extends for 500 miles along the coast, and probably for a
considerably greater distance. At Port St. Julian its thickness is
more than 800 feet! These white beds are everywhere capped by a
mass of gravel, forming probably one of the largest beds of shingle
in the world: it certainly extends from near the Rio Colorado to
between 600 and 700 nautical miles southward, at Santa Cruz (a
river a little south of St. Julian) it reaches to the foot of the
Cordillera; half way up the river its thickness is more than 200
feet; it probably everywhere extends to this great chain, whence
the well-rounded pebbles of porphyry have been derived: we may
consider its average breadth as 200 miles, and its average
thickness as about 50 feet. If this great bed of pebbles, without
including the mud necessarily derived from their attrition, was
piled into a mound, it would form a great mountain chain! When we
consider that all these pebbles, countless as the grains of sand in
the desert, have been derived from the slow falling of masses of
rock on the old coast-lines and banks of rivers, and that these
fragments have been dashed into smaller pieces, and that each of
them has since been slowly rolled, rounded, and far transported,
the mind is stupefied in thinking over the long, absolutely
necessary, lapse of years. Yet all this gravel has been
transported, and probably rounded, subsequently to the deposition
of the white beds, and long subsequently to the underlying beds
with the tertiary shells.

Everything in this southern continent has been effected on a grand
scale: the land, from the Rio Plata to Tierra del Fuego, a distance
of 1200 miles, has been raised in mass (and in Patagonia to a
height of between 300 and 400 feet), within the period of the now
existing sea-shells. The old and weathered shells left on the
surface of the upraised plain still partially retain their colours.
The uprising movement has been interrupted by at least eight long
periods of rest, during which the sea ate deeply back into the
land, forming at successive levels the long lines of cliffs or
escarpments, which separate the different plains as they rise like
steps one behind the other. The elevatory movement, and the
eating-back power of the sea during the periods of rest, have been
equable over long lines of coast; for I was astonished to find that
the step-like plains stand at nearly corresponding heights at far
distant points. The lowest plain is 90 feet high; and the highest,
which I ascended near the coast, is 950 feet; and of this only
relics are left in the form of flat gravel-capped hills. The upper
plain of Santa Cruz slopes up to a height of 3000 feet at the foot
of the Cordillera. I have said that within the period of existing
sea-shells, Patagonia has been upraised 300 to 400 feet: I may add,
that within the period when icebergs transported boulders over the
upper plain of Santa Cruz, the elevation has been at least 1500
feet. Nor has Patagonia been affected only by upward movements: the
extinct tertiary shells from Port St. Julian and Santa Cruz cannot
have lived, according to Professor E. Forbes, in a greater depth of
water than from 40 to 250 feet; but they are now covered with
sea-deposited strata from 800 to 1000 feet in thickness: hence the
bed of the sea, on which these shells once lived, must have sunk
downwards several hundred feet, to allow of the accumulation of the
superincumbent strata. What a history of geological changes does
the simply-constructed coast of Patagonia reveal!


At Port St. Julian, in some red mud capping the gravel on the
90-feet plain, I found half the skeleton of the Macrauchenia
Patachonica, a remarkable quadruped, full as large as a camel.
(8/12. I have lately heard that Captain Sulivan, R.N., has found
numerous fossil bones, embedded in regular strata, on the banks of
the R. Gallegos, in latitude 51 degrees 4'. Some of the bones are
large; others are small, and appear to have belonged to an
armadillo. This is a most interesting and important discovery.) It
belongs to the same division of the Pachydermata with the
rhinoceros, tapir, and palaeotherium; but in the structure of the
bones of its long neck it shows a clear relation to the camel, or
rather to the guanaco and llama. From recent sea-shells being found
on two of the higher step-formed plains, which must have been
modelled and upraised before the mud was deposited in which the
Macrauchenia was intombed, it is certain that this curious
quadruped lived long after the sea was inhabited by its present
shells. I was at first much surprised how a large quadruped could
so lately have subsisted, in latitude 49 degrees 15', on these
wretched gravel plains with their stunted vegetation; but the
relationship of the Macrauchenia to the Guanaco, now an inhabitant
of the most sterile parts, partly explains this difficulty.

The relationship, though distant, between the Macrauchenia and the
Guanaco, between the Toxodon and the Capybara, - the closer
relationship between the many extinct Edentata and the living
sloths, ant-eaters, and armadillos, now so eminently characteristic
of South American zoology, - and the still closer relationship
between the fossil and living species of Ctenomys and Hydrochaerus,
are most interesting facts. This relationship is shown
wonderfully - as wonderfully as between the fossil and extinct
Marsupial animals of Australia - by the great collection lately
brought to Europe from the caves of Brazil by MM. Lund and Clausen.
In this collection there are extinct species of all the thirty-two
genera, excepting four, of the terrestrial quadrupeds now
inhabiting the provinces in which the caves occur; and the extinct
species are much more numerous than those now living: there are
fossil ant-eaters, armadillos, tapirs, peccaries, guanacos,
opossums, and numerous South American gnawers and monkeys, and
other animals. This wonderful relationship in the same continent
between the dead and the living, will, I do not doubt, hereafter
throw more light on the appearance of organic beings on our earth,
and their disappearance from it, than any other class of facts.

It is impossible to reflect on the changed state of the American
continent without the deepest astonishment. Formerly it must have
swarmed with great monsters: now we find mere pigmies, compared
with the antecedent allied races. If Buffon had known of the
gigantic sloth and armadillo-like animals, and of the lost
Pachydermata, he might have said with a greater semblance of truth
that the creative force in America had lost its power, rather than
that it had never possessed great vigour. The greater number, if
not all, of these extinct quadrupeds lived at a late period, and
were the contemporaries of most of the existing sea-shells. Since
they lived, no very great change in the form of the land can have
taken place. What, then, has exterminated so many species and whole
genera? The mind at first is irresistibly hurried into the belief
of some great catastrophe; but thus to destroy animals, both large
and small, in Southern Patagonia, in Brazil, on the Cordillera of
Peru, in North America up to Behring's Straits, we must shake the
entire framework of the globe. An examination, moreover, of the
geology of La Plata and Patagonia, leads to the belief that all the
features of the land result from slow and gradual changes. It
appears from the character of the fossils in Europe, Asia,
Australia, and in North and South America, that those conditions
which favour the life of the LARGER quadrupeds were lately
coextensive with the world: what those conditions were, no one has
yet even conjectured. It could hardly have been a change of
temperature, which at about the same time destroyed the inhabitants
of tropical, temperate, and arctic latitudes on both sides of the
globe. In North America we positively know from Mr. Lyell that the
large quadrupeds lived subsequently to that period, when boulders
were brought into latitudes at which icebergs now never arrive:
from conclusive but indirect reasons we may feel sure, that in the
southern hemisphere the Macrauchenia, also, lived long subsequently
to the ice-transporting boulder-period. Did man, after his first
inroad into South America, destroy, as has been suggested, the
unwieldy Megatherium and the other Edentata? We must at least look
to some other cause for the destruction of the little tucutuco at
Bahia Blanca, and of the many fossil mice and other small
quadrupeds in Brazil. No one will imagine that a drought, even far
severer than those which cause such losses in the provinces of La
Plata, could destroy every individual of every species from
Southern Patagonia to Behring's Straits. What shall we say of the
extinction of the horse? Did those plains fail of pasture, which
have since been overrun by thousands and hundreds of thousands of
the descendants of the stock introduced by the Spaniards? Have the
subsequently introduced species consumed the food of the great
antecedent races? Can we believe that the Capybara has taken the
food of the Toxodon, the Guanaco of the Macrauchenia, the existing
small Edentata of their numerous gigantic prototypes? Certainly, no
fact in the long history of the world is so startling as the wide
and repeated exterminations of its inhabitants.

Nevertheless, if we consider the subject under another point of
view, it will appear less perplexing. We do not steadily bear in
mind how profoundly ignorant we are of the conditions of existence
of every animal; nor do we always remember that some check is
constantly preventing the too rapid increase of every organised
being left in a state of nature. The supply of food, on an average,
remains constant, yet the tendency in every animal to increase by
propagation is geometrical; and its surprising effects have nowhere
been more astonishingly shown, than in the case of the European
animals run wild during the last few centuries in America. Every
animal in a state of nature regularly breeds; yet in a species long
established, any GREAT increase in numbers is obviously impossible,
and must be checked by some means. We are, nevertheless, seldom
able with certainty to tell in any given species, at what period of
life, or at what period of the year, or whether only at long
intervals, the check falls; or, again, what is the precise nature
of the check. Hence probably it is that we feel so little surprise
at one, of two species closely allied in habits, being rare and the
other abundant in the same district; or, again, that one should be
abundant in one district, and another, filling the same place in
the economy of nature, should be abundant in a neighbouring
district, differing very little in its conditions. If asked how
this is, one immediately replies that it is determined by some
slight difference in climate, food, or the number of enemies: yet
how rarely, if ever, we can point out the precise cause and manner
of action of the check! We are therefore, driven to the conclusion
that causes generally quite inappreciable by us, determine whether
a given species shall be abundant or scanty in numbers.

In the cases where we can trace the extinction of a species through
man, either wholly or in one limited district, we know that it
becomes rarer and rarer, and is then lost: it would be difficult to
point out any just distinction between a species destroyed by man
or by the increase of its natural enemies. (8/13. See the excellent
remarks on this subject by Mr. Lyell in his "Principles of
Geology.") The evidence of rarity preceding extinction is more
striking in the successive tertiary strata, as remarked by several
able observers; it has often been found that a shell very common in
a tertiary stratum is now most rare, and has even long been thought
to be extinct. If then, as appears probable, species first become
rare and then extinct - if the too rapid increase of every species,
even the most favoured, is steadily checked, as we must admit,
though how and when it is hard to say - and if we see, without the
smallest surprise, though unable to assign the precise reason, one
species abundant and another closely-allied species rare in the
same district - why should we feel such great astonishment at the
rarity being carried a step farther to extinction? An action going
on, on every side of us, and yet barely appreciable, might surely
be carried a little farther without exciting our observation. Who
would feel any great surprise at hearing that the Magalonyx was
formerly rare compared with the Megatherium, or that one of the
fossil monkeys was few in number compared with one of the now
living monkeys? and yet in this comparative rarity, we should have
the plainest evidence of less favourable conditions for their
existence. To admit that species generally become rare before they
become extinct - to feel no surprise at the comparative rarity of
one species with another, and yet to call in some extraordinary
agent and to marvel greatly when a species ceases to exist, appears
to me much the same as to admit that sickness in the individual is
the prelude to death - to feel no surprise at sickness - but when the
sick man dies to wonder, and to believe that he died through



(PLATE 41. CONDOR (Sarcorhamphus gryphus).)

Santa Cruz.
Expedition up the River.
Immense Streams of basaltic lava.
Fragments not transported by the River.
Excavation of the valley.
Condor, habits of.
Erratic boulders of great size.
Indian relics.
Return to the ship.
Falkland Islands.
Wild horses, cattle, rabbits.
Wolf-like fox.
Fire made of bones.
Manner of hunting wild cattle.
Streams of stones.
Scenes of violence.
Eggs of Doris.
Compound animals.


APRIL 13, 1834.

The "Beagle" anchored within the mouth of the Santa Cruz. This
river is situated about sixty miles south of Port St. Julian.
During the last voyage Captain Stokes proceeded thirty miles up it,
but then, from the want of provisions, was obliged to return.
Excepting what was discovered at that time, scarcely anything was
known about this large river. Captain Fitz Roy now determined to
follow its course as far as time would allow. On the 18th three
whale-boats started, carrying three weeks' provisions; and the
party consisted of twenty-five souls - a force which would have been
sufficient to have defied a host of Indians. With a strong
flood-tide and a fine day we made a good run, soon drank some of
the fresh water, and were at night nearly above the tidal

The river here assumed a size and appearance which, even at the
highest point we ultimately reached, was scarcely diminished. It
was generally from three to four hundred yards broad, and in the
middle about seventeen feet deep. The rapidity of the current,
which in its whole course runs at the rate of from four to six
knots an hour, is perhaps its most remarkable feature. The water is
of a fine blue colour, but with a slight milky tinge, and not so
transparent as at first sight would have been expected. It flows
over a bed of pebbles, like those which compose the beach and the
surrounding plains. It runs in a winding course through a valley,
which extends in a direct line westward. This valley varies from
five to ten miles in breadth; it is bounded by step-formed
terraces, which rise in most parts, one above the other, to the
height of five hundred feet, and have on the opposite sides a
remarkable correspondence.

APRIL 19, 1834.

Against so strong a current it was, of course, quite impossible to
row or sail: consequently the three boats were fastened together
head and stern, two hands left in each, and the rest came on shore
to track. As the general arrangements made by Captain Fitz Roy were
very good for facilitating the work of all, and as all had a share
in it, I will describe the system. The party, including every one,
was divided into two spells, each of which hauled at the tracking
line alternately for an hour and a half. The officers of each boat
lived with, ate the same food, and slept in the same tent with
their crew, so that each boat was quite independent of the others.
After sunset the first level spot where any bushes were growing was
chosen for our night's lodging. Each of the crew took it in turns
to be cook. Immediately the boat was hauled up, the cook made his
fire; two others pitched the tent; the coxswain handed the things
out of the boat; the rest carried them up to the tents and
collected firewood. By this order, in half an hour everything was
ready for the night. A watch of two men and an officer was always
kept, whose duty it was to look after the boats, keep up the fire,
and guard against Indians. Each in the party had his one hour every

During this day we tracked but a short distance, for there were
many islets, covered by thorny bushes, and the channels between
them were shallow.

APRIL 20, 1834.

We passed the islands and set to work. Our regular day's march,
although it was hard enough, carried us on an average only ten
miles in a straight line, and perhaps fifteen or twenty altogether.
Beyond the place where we slept last night, the country is
completely terra incognita, for it was there that Captain Stokes
turned back. We saw in the distance a great smoke, and found the
skeleton of a horse, so we knew that Indians were in the
neighbourhood. On the next morning (21st) tracks of a party of
horse, and marks left by the trailing of the chuzos, or long
spears, were observed on the ground. It was generally thought that
the Indians had reconnoitred us during the night. Shortly
afterwards we came to a spot where, from the fresh footsteps of
men, children, and horses, it was evident that the party had
crossed the river.

APRIL 22, 1834.

The country remained the same, and was extremely uninteresting. The
complete similarity of the productions throughout Patagonia is one
of its most striking characters. The level plains of arid shingle
support the same stunted and dwarf plants; and in the valleys the
same thorn-bearing bushes grow. Everywhere we see the same birds
and insects. Even the very banks of the river and of the clear
streamlets which entered it, were scarcely enlivened by a brighter
tint of green. The curse of sterility is on the land, and the water
flowing over a bed of pebbles partakes of the same curse. Hence the
number of waterfowl is very scanty; for there is nothing to support
life in the stream of this barren river.

Patagonia, poor as she is in some respects, can however boast of a
greater stock of small rodents than perhaps any other country in
the world. (9/1. The desserts of Syria are characterised, according
to Volney tome 1 page 351, by woody bushes, numerous rats, gazelles
and hares. In the landscape of Patagonia the guanaco replaces the
gazelle, and the agouti the hare.) Several species of mice are
externally characterised by large thin ears and a very fine fur.
These little animals swarm amongst the thickets in the valleys,
where they cannot for months together taste a drop of water
excepting the dew. They all seem to be cannibals; for no sooner was
a mouse caught in one of my traps than it was devoured by others. A
small and delicately-shaped fox, which is likewise very abundant,
probably derives its entire support from these small animals. The
guanaco is also in his proper district, herds of fifty or a hundred
were common; and, as I have stated, we saw one which must have
contained at least five hundred. The puma, with the condor and
other carrion-hawks in its train, follows and preys upon these
animals. The footsteps of the puma were to be seen almost
everywhere on the banks of the river; and the remains of several
guanacos, with their necks dislocated and bones broken, showed how
they had met their death.

APRIL 24, 1834.

Like the navigators of old when approaching an unknown land, we
examined and watched for the most trivial sign of a change. The
drifted trunk of a tree, or a boulder of primitive rock, was hailed
with joy, as if we had seen a forest growing on the flanks of the
Cordillera. The top, however, of a heavy bank of clouds, which
remained almost constantly in one position, was the most promising
sign, and eventually turned out a true harbinger. At first the
clouds were mistaken for the mountains themselves, instead of the
masses of vapour condensed by their icy summits.

APRIL 26, 1834.

We this day met with a marked change in the geological structure of
the plains. From the first starting I had carefully examined the
gravel in the river, and for the two last days had noticed the
presence of a few small pebbles of a very cellular basalt. These
gradually increased in number and in size, but none were as large
as a man's head. This morning, however, pebbles of the same rock,
but more compact, suddenly became abundant, and in the course of
half an hour we saw, at the distance of five or six miles, the
angular edge of a great basaltic platform. When we arrived at its
base we found the stream bubbling among the fallen blocks. For the
next twenty-eight miles the river-course was encumbered with these
basaltic masses. Above that limit immense fragments of primitive
rocks, derived from the surrounding boulder-formation, were equally
numerous. None of the fragments of any considerable size had been
washed more than three or four miles down the river below their
parent-source: considering the singular rapidity of the great body
of water in the Santa Cruz, and that no still reaches occur in any
part, this example is a most striking one, of the inefficiency of
rivers in transporting even moderately-sized fragments.

The basalt is only lava which has flowed beneath the sea; but the
eruptions must have been on the grandest scale. At the point where
we first met this formation it was 120 feet in thickness; following
up the river-course, the surface imperceptibly rose and the mass
became thicker, so that at forty miles above the first station it
was 320 feet thick. What the thickness may be close to the
Cordillera, I have no means of knowing, but the platform there
attains a height of about three thousand feet above the level of
the sea: we must therefore look to the mountains of that great
chain for its source; and worthy of such a source are streams that
have flowed over the gently inclined bed of the sea to a distance
of one hundred miles. At the first glance of the basaltic cliffs on
the opposite sides of the valley it was evident that the strata
once were united. What power, then, has removed along a whole line
of country a solid mass of very hard rock, which had an average
thickness of nearly three hundred feet, and a breadth varying from
rather less than two miles to four miles? The river, though it has
so little power in transporting even inconsiderable fragments, yet
in the lapse of ages might produce by its gradual erosion an
effect, of which it is difficult to judge the amount. But in this
case, independently of the insignificance of such an agency, good
reasons can be assigned for believing that this valley was formerly
occupied by an arm of the sea. It is needless in this work to
detail the arguments leading to this conclusion, derived from the
form and the nature of the step-formed terraces on both sides of

Online LibraryCharles DarwinThe Voyage of the Beagle → online text (page 18 of 51)