More Letters of Charles Darwin Volume I

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"Formerly Milton's "Paradise Lost" had been my chief favourite, and in my
excursions during the voyage of the 'Beagle,' when I could take only a
single volume, I always chose Milton" ("Autobiography," page 69).);
its colours are by Werner (4/3. Werner's "Nomenclature of Colours,"
Edinburgh, 1821.) ink black, vermilion red and buff orange. It has been a
splendid cruise for me in Nat. History. Amongst the Pelagic Crustacea,
some new and curious genera. In the Zoophytes some interesting animals.
As for one Flustra, if I had not the specimen to back me up nobody would
believe in its most anomalous structure. But as for novelty all this is
nothing to a family of pelagic animals which at first sight appear like
Medusae but are really highly organised. I have examined them repeatedly,
and certainly from their structure it would be impossible to place them in
any existing order. Perhaps Salpa is the nearest animal, although the
transparency of the body is nearly the only character they have in common.
I think the dried plants nearly contain all which were then (Bahia Blanca)
flowering. All the specimens will be packed in casks. I think there will
be three (before sending this letter I will specify dates, etc., etc.). I
am afraid you will groan or rather the floor of the lecture room will when
the casks arrive. Without you I should be utterly undone. The small cask
contains fish: will you open it to see how the spirit has stood the
evaporation of the Tropics. On board the ship everything goes on as well
as possible; the only drawback is the fearful length of time between this
and the day of our return. I do not see any limits to it. One year is
nearly completed and the second will be so, before we even leave the east
coast of S. America. And then our voyage may be said really to have
commenced. I know not how I shall be able to endure it. The frequency
with which I think of all the happy hours I have spent at Shrewsbury and
Cambridge is rather ominous--I trust everything to time and fate and will
feel my way as I go on.

November 24th.--We have been at Buenos Ayres for a week; it is a fine large
city, but such a country, everything is mud, you can go nowhere, you can do
nothing for mud. In the city I obtained much information about the banks
of the Uruguay--I hear of limestone with shells, and beds of shells in
every direction. I hope when we winter in the Plata to have a most
interesting geological excursion into that country: I purchased fragments
(Nos. 837-8) of some enormous bones, which I was assured belonged to the
former giants!! I also procured some seeds--I do not know whether they are
worth your accepting; if you think so I will get some more. They are in
the box. I have sent to you by the "Duke of York" packet, commanded by
Lieut. Snell, to Falmouth two large casks containing fossil bones, a small
cask with fish and a box containing skins, spirit bottle, etc., and pill-
boxes with beetles. Would you be kind enough to open these latter as they
are apt to become mouldy. With the exception of the bones the rest of my
collection looks very scanty. Recollect how great a proportion of time is
spent at sea. I am always anxious to hear in what state the things come
and any criticisms about quantity or kind of specimens. In the smaller
cask is part of a large head, the anterior portions of which are in the
other large one. The packet has arrived and I am in a great bustle. You
will not hear from me for some months.

LETTER 5. TO J.S. HENSLOW.
Valparaiso, July 24th 1834.

A box has just arrived in which were two of your most kind and affectionate
letters. You do not know how happy they have made me. One is dated
December 15th, 1833, the other January 15th of the same year! By what
fatality it did not arrive sooner I cannot conjecture; I regret it much,
for it contains the information I most wanted, about manner of packing,
etc., etc.: roots with specimens of plants, etc., etc. This I suppose was
written after the reception of my first cargo of specimens. Not having
heard from you until March of this year I really began to think that my
collections were so poor, that you were puzzled what to say; the case is
now quite on the opposite tack; for you are guilty of exciting all my vain
feelings to a most comfortable pitch; if hard work will atone for these
thoughts, I vow it shall not be spared. It is rather late, but I will
allude to some remarks in the January letter; you advise me to send home
duplicates of my notes; I have been aware of the advantage of doing so; but
then at sea to this day, I am invariably sick, excepting on the finest
days, at which times with pelagic animals around me, I could never bring
myself to the task--on shore the most prudent person could hardly expect
such a sacrifice of time. My notes are becoming bulky. I have about 600
small quarto pages full; about half of this is Geology--the other imperfect
descriptions of animals; with the latter I make it a rule only to describe
those parts or facts, which cannot be seen in specimens in spirits. I keep
my private Journal distinct from the above. (N.B. this letter is a most
untidy one, but my mind is untidy with joy; it is your fault, so you must
take the consequences.) With respect to the land Planariae, unquestionably
they are not molluscous animals. I read your letters last night, this
morning I took a little walk; by a curious coincidence, I found a new white
species of Planaria, and a new to me Vaginulus (third species which I have
found in S. America) of Cuvier. Amongst the marine mollusques I have seen
a good many genera, and at Rio found one quite new one. With respect to
the December letter, I am very glad to hear the four casks arrived safe;
since which time you have received another cargo, with the bird skins about
which you did not understand me. Have any of the B. Ayrean seeds produced
plants? From the Falklands I acknowledged a box and letter from you; with
the letter were a few seeds from Patagonia. At present I have specimens
enough to make a heavy cargo, but shall wait as much longer as possible,
because opportunities are not now so good as before. I have just got scent
of some fossil bones of a MAMMOTH; what they may be I do not know, but if
gold or galloping will get them they shall be mine. You tell me you like
hearing how I am going on and what doing, and you well may imagine how much
I enjoy speaking to any one upon subjects which I am always thinking about,
but never have any one to talk to [about]. After leaving the Falklands we
proceeded to the Rio S. Cruz, following up the river till within twenty
miles of the Cordilleras. Unfortunately want of provisions compelled us to
return. This expedition was most important to me as it was a transverse
section of the great Patagonian formation. I conjecture (an accurate
examination of fossils may possibly determine the point) that the main bed
is somewhere about the Miocene period (using Mr. Lyell's expression); I
judge from what I have seen of the present shells of Patagonia. This bed
contains an ENORMOUS field of lava. This is of some interest, as being a
rude approximation to the age of the volcanic part of the great range of
the Andes. Long before this it existed as a slate and porphyritic line of
hills. I have collected a tolerable quantity of information respecting the
period and forms of elevations of these plains. I think these will be
interesting to Mr. Lyell; I had deferred reading his third volume till my
return: you may guess how much pleasure it gave me; some of his woodcuts
came so exactly into play that I have only to refer to them instead of
redrawing similar ones. I had my barometer with me, I only wish I had used
it more in these plains. The valley of S. Cruz appears to me a very
curious one; at first it quite baffled me. I believe I can show good
reasons for supposing it to have been once a northern straits like to that
of Magellan. When I return to England you will have some hard work in
winnowing my Geology; what little I know I have learnt in such a curious
fashion that I often feel very doubtful about the number of grains [of
value?]. Whatever number they may turn out, I have enjoyed extreme
pleasure in collecting them. In T. del Fuego I collected and examined some
corallines; I have observed one fact which quite startled me: it is that
in the genus Sertularia (taken in its most restricted form as [used] by
Lamoureux) and in two species which, excluding comparative expressions, I
should find much difficulty in describing as different, the polypi quite
and essentially differed in all their most important and evident parts of
structure. I have already seen enough to be convinced that the present
families of corallines as arranged by Lamarck, Cuvier, etc., are highly
artificial. It appears that they are in the same state [in] which shells
were when Linnaeus left them for Cuvier to rearrange. I do so wish I was a
better hand at dissecting, I find I can do very little in the minute parts
of structure; I am forced to take a very rough examination as a type for
different classes of structure. It is most extraordinary I can nowhere see
in my books one single description of the polypus of any one coralline
excepting Alcyonium Lobularia of Savigny. I found a curious little stony
Cellaria (5/1. Cellaria, a genus of Bryozoa, placed in the section
Flustrina of the Suborder Chilostomata.) (a new genus) each cell provided
with long toothed bristle, these are capable of various and rapid motions.
This motion is often simultaneous, and can be produced by irritation. This
fact, as far as I can see, is quite isolated in the history of zoophytes
(excepting the Flustra with an organ like a vulture's head); it points out
a much more intimate relation between the polypi than Lamarck is willing to
allow. I forgot whether I mentioned having seen something of the manner of
propagation in that most ambiguous family, the corallines; I feel pretty
well convinced if they are not plants they are not zoophytes. The
"gemmule" of a Halimeda contained several articulations united, ready to
burst their envelope, and become attached to some basis. I believe in
zoophytes universally the gemmule produces a single polypus, which
afterwards or at the same time grows with its cell or single articulation.

The "Beagle" left the Sts. of Magellan in the middle of winter; she found
her road out by a wild unfrequented channel; well might Sir J. Narborough
call the west coast South Desolation, "because it is so desolate a land to
behold." We were driven into Chiloe by some very bad weather. An
Englishman gave me three specimens of that very fine Lucanoidal insect
which is described in the "Camb. Phil. Trans." (5/2. "Description of
Chiasognathus Grantii, a new Lucanideous Insect, etc." by J.F. Stephens
("Trans. Camb. Phil. Soc." Volume IV., page 209, 1833.), two males and one
female. I find Chiloe is composed of lava and recent deposits. The lavas
are curious from abounding in, or rather being in parts composed of
pitchstone. If we go to Chiloe in the summer, I shall reap an
entomological harvest. I suppose the Botany both there and in Chili is
well-known.

I forgot to state that in the four cargoes of specimens there have been
sent three square boxes, each containing four glass bottles. I mention
this in case they should be stowed beneath geological specimens and thus
escape your notice, perhaps some spirit may be wanted in them. If a box
arrives from B. Ayres with a Megatherium head the other unnumbered
specimens, be kind enough to tell me, as I have strong fears for its
safety. We arrived here the day before yesterday; the views of the distant
mountains are most sublime and the climate delightful; after our long
cruise in the damp gloomy climates of the south, to breathe a clear dry air
and feel honest warm sunshine, and eat good fresh roast beef must be the
summum bonum of human life. I do not like the look of the rocks half so
much as the beef, there is too much of those rather insipid ingredients,
mica, quartz and feldspar. Our plans are at present undecided; there is a
good deal of work to the south of Valparaiso and to the north an indefinite
quantity. I look forward to every part with interest. I have sent you in
this letter a sad dose of egotism, but recollect I look up to you as my
father in Natural History, and a son may talk about himself to his father.
In your paternal capacity as proproctor what a great deal of trouble you
appear to have had. How turbulent Cambridge is become. Before this time
it will have regained its tranquillity. I have a most schoolboy-like wish
to be there, enjoying my holidays. It is a most comfortable reflection to
me, that a ship being made of wood and iron, cannot last for ever, and
therefore this voyage must have an end.

October 28th. This letter has been lying in my portfolio ever since July;
I did not send it away because I did not think it worth the postage; it
shall now go with a box of specimens. Shortly after arriving here I set
out on a geological excursion, and had a very pleasant ramble about the
base of the Andes. The whole country appears composed of breccias (and I
imagine slates) which universally have been modified and oftentimes
completely altered by the action of fire. The varieties of porphyry thus
produced are endless, but nowhere have I yet met with rocks which have
flowed in a stream; dykes of greenstone are very numerous. Modern volcanic
action is entirely shut up in the very central parts (which cannot now be
reached on account of the snow) of the Cordilleras. In the south of the R.
Maypu I examined the Tertiary plains, already partially described by M.
Gay. (5/3. "Rapport fait a l'Academie Royale des Sciences, sur les
Travaux Geologiques de M. Gay," by Alex. Brongniart ("Ann. Sci. Nat."
Volume XXVIII., page 394, 1833.) The fossil shells appear to me to be far
more different from the recent ones than in the great Patagonian formation;
it will be curious if an Eocene and Miocene (recent there is abundance of)
could be proved to exist in S. America as well as in Europe. I have been
much interested by finding abundance of recent shells at an elevation of
1,300 feet; the country in many places is scattered over with shells but
these are all littoral ones. So that I suppose the 1,300 feet elevation
must be owing to a succession of small elevations such as in 1822. With
these certain proofs of the recent residence of the ocean over all the
lower parts of Chili, the outline of every view and the form of each valley
possesses a high interest. Has the action of running water or the sea
formed this deep ravine? was a question which often arose in my mind and
generally was answered by finding a bed of recent shells at the bottom. I
have not sufficient arguments, but I do not believe that more than a small
fraction of the height of the Andes has been formed within the Tertiary
period. The conclusion of my excursion was very unfortunate, I became
unwell and could hardly reach this place. I have been in bed for the last
month, but am now rapidly getting well. I had hoped during this time to
have made a good collection of insects but it has been impossible: I
regret the less because Chiloe fairly swarms with collectors; there are
more naturalists in the country, than carpenters or shoemakers or any other
honest trade.

In my letter from the Falkland Islands I said I had fears about a box with
a Megatherium. I have since heard from B. Ayres that it went to Liverpool
by the brig "Basingwaithe." If you have not received it, it is I think
worth taking some trouble about. In October two casks and a jar were sent
by H.M.S. "Samarang" via Portsmouth. I have no doubt you have received
them. With this letter I send a good many bird skins; in the same box with
them, there is a paper parcel containing pill boxes with insects. The
other pill boxes require no particular care. You will see in two of these
boxes some dried Planariae (terrestrial), the only method I have found of
preserving them (they are exceedingly brittle). By examining the white
species I understand some little of the internal structure. There are two
small parcels of seeds. There are some plants which I hope may interest
you, or at least those from Patagonia where I collected every one in
flower. There is a bottle clumsily but I think securely corked containing
water and gas from the hot baths of Cauquenes seated at foot of Andes and
long celebrated for medicinal properties. I took pains in filling and
securing both water and gas. If you can find any one who likes to analyze
them, I should think it would be worth the trouble. I have not time at
present to copy my few observations about the locality, etc., etc., [of]
these springs. Will you tell me how the Arachnidae which I have sent home,
for instance those from Rio, appear to be preserved. I have doubts whether
it is worth while collecting them.

We sail the day after to-morrow: our plans are at last limited and
definite; I am delighted to say we have bid an eternal adieu to T. del
Fuego. The "Beagle" will not proceed further south than C. Tres Montes;
from which point we survey to the north. The Chonos Archipelago is
delightfully unknown: fine deep inlets running into the Cordilleras--where
we can steer by the light of a volcano. I do not know which part of the
voyage now offers the most attractions. This is a shamefully untidy
letter, but you must forgive me.

LETTER 6. TO J.S. HENSLOW.
April 18th, 1835. Valparaiso.

I have just returned from Mendoza, having crossed the Cordilleras by two
passes. This trip has added much to my knowledge of the geology of the
country. Some of the facts, of the truth of which I in my own mind feel
fully convinced, will appear to you quite absurd and incredible. I will
give a very short sketch of the structure of these huge mountains. In the
Portillo pass (the more southern one) travellers have described the
Cordilleras to consist of a double chain of nearly equal altitude separated
by a considerable interval. This is the case; and the same structure
extends to the northward to Uspallata; the little elevation of the eastern
line (here not more than 6,000-7,000 feet.) has caused it almost to be
overlooked. To begin with the western and principal chain, we have, where
the sections are best seen, an enormous mass of a porphyritic conglomerate
resting on granite. This latter rock seems to form the nucleus of the
whole mass, and is seen in the deep lateral valleys, injected amongst,
upheaving, overturning in the most extraordinary manner, the overlying
strata. The stratification in all the mountains is beautifully distinct
and from a variety in the colour can be seen at great distances. I cannot
imagine any part of the world presenting a more extraordinary scene of the
breaking up of the crust of the globe than the very central parts of the
Andes. The upheaval has taken place by a great number of (nearly) N. and
S. lines; which in most cases have formed as many anticlinal and synclinal
ravines; the strata in the highest pinnacles are almost universally
inclined at an angle from 70 deg to 80 deg. I cannot tell you how I
enjoyed some of these views--it is worth coming from England, once to feel
such intense delight; at an elevation from 10 to 12,000 feet there is a
transparency in the air, and a confusion of distances and a sort of
stillness which gives the sensation of being in another world, and when to
this is joined the picture so plainly drawn of the great epochs of
violence, it causes in the mind a most strange assemblage of ideas.

The formation I call Porphyritic Conglomerates is the most important and
most developed one in Chili: from a great number of sections I find it a
true coarse conglomerate or breccia, which by every step in a slow
gradation passes into a fine claystone-porphyry; the pebbles and cement
becoming porphyritic till at last all is blended in one compact rock. The
porphyries are excessively abundant in this chain. I feel sure at least
4/5ths of them have been thus produced from sedimentary beds in situ.
There are porphyries which have been injected from below amongst strata,
and others ejected, which have flowed in streams; it is remarkable, and I
could show specimens of this rock produced in these three methods, which
cannot be distinguished. It is a great mistake considering the Cordilleras
here as composed of rocks which have flowed in streams. In this range I
nowhere saw a fragment, which I believe to have thus originated, although
the road passes at no great distance from the active volcanoes. The
porphyries, conglomerate, sandstone and quartzose sandstone and limestones
alternate and pass into each other many times, overlying (where not broken
through by the granite) clay-slate. In the upper parts, the sandstone
begins to alternate with gypsum, till at last we have this substance of a
stupendous thickness. I really think the formation is in some places (it
varies much) nearly 2,000 feet thick, it occurs often with a green
(epidote?) siliceous sandstone and snow-white marble; it resembles that
found in the Alps in containing large concretions of a crystalline marble
of a blackish grey colour. The upper beds which form some of the higher
pinnacles consist of layers of snow-white gypsum and red compact sandstone,
from the thickness of paper to a few feet, alternating in an endless round.
The rock has a most curiously painted appearance. At the pass of the
Peuquenes in this formation, where however a black rock like clay-slate,
without many laminae, occurring with a pale limestone, has replaced the red
sandstone, I found abundant impressions of shells. The elevation must be
between 12 and 13,000 feet. A shell which I believe is the Gryphaea is the
most abundant--an Ostrea, Turratella, Ammonites, small bivalves,
Terebratulae (?). Perhaps some good conchologist (6/1. Some of these
genera are mentioned by Darwin ("Geol. Obs." page 181) as having been named
for him by M. D'Orbigny.) will be able to give a guess, to what grand
division of the formations of Europe these organic remains bear most
resemblance. They are exceedingly imperfect and few. It was late in the
season and the situation particularly dangerous for snow-storms. I did not
dare to delay, otherwise a grand harvest might have been reaped. So much
for the western line; in the Portillo pass, proceeding eastward, we meet an
immense mass of conglomerate, dipping to the west 45 deg, which rest on
micaceous sandstone, etc., etc., upheaved and converted into quartz-rock
penetrated by dykes from the very grand mass of protogine (large crystals
of quartz, red feldspar, and occasional little chlorite). Now this
conglomerate which reposes on and dips from the protogene 45 deg consists
of the peculiar rocks of the first described chain, pebbles of the black
rock with shells, green sandstone, etc., etc. It is hence manifest that
the upheaval (and deposition at least of part) of the grand eastern chain
is entirely posterior to the western. To the north in the Uspallata pass,
we have also a fact of the same class. Bear this in mind: it will help to
make you believe what follows. I have said the Uspallata range is
geologically, although only 6,000-7,000 feet, a continuation of the grand
eastern chain. It has its nucleus of granite, consists of grand beds of
various crystalline rocks, which I can feel no doubt are subaqueous lavas
alternating with sandstone, conglomerates and white aluminous beds (like
decomposed feldspar) with many other curious varieties of sedimentary
deposits. These lavas and sandstones alterate very many times, and are
quite conformable one to the other. During two days of careful examination
I said to myself at least fifty times, how exactly like (only rather
harder) these beds are to those of the upper Tertiary strata of Patagonia,
Chiloe and Concepcion, without the possible identity ever having occurred
to me. At last there was no resisting the conclusion. I could not expect
shells, for they never occur in this formation; but lignite or carbonaceous
shale ought to be found. I had previously been exceedingly puzzled by
meeting in the sandstone, thin layers (few inches to feet thick) of a
brecciated pitchstone. I strongly suspect the underlying granite has
altered such beds into this pitchstone. The silicified wood (particularly
characteristic) was yet absent. The conviction that I was on the Tertiary
strata was so strong by this time in my mind, that on the third day in the
midst of lavas and [? masses] of granite I began my apparently forlorn
hunt. How do you think I succeeded? In an escarpement of compact greenish
sandstone, I found a small wood of petrified trees in a vertical position,
or rather the strata were inclined about 20-30 deg to one point and the
trees 70 deg to the opposite one. That is, they were before the tilt truly
vertical. The sandstone consists of many layers, and is marked by the
concentric lines of the bark (I have specimens); 11 are perfectly
silicified and resemble the dicotyledonous wood which I have found at
Chiloe and Concepcion (6/2. "Geol. Obs." page 202. Specimens of the
silicified wood were examined by Robert Brown, and determined by him as
coniferous, "partaking of the characters of the Araucarian tribe, with some
curious points of affinity with the yew."); the others (30-40) I only know
to be trees from the analogy of form and position; they consist of snow-
white columns (like Lot's wife) of coarsely crystalline carb. of lime. The
largest shaft is 7 feet. They are all close together, within 100 yards,
and about the same level: nowhere else could I find any. It cannot be
doubted that the layers of fine sandstone have quietly been deposited
between a clump of trees which were fixed by their roots. The sandstone
rests on lava, is covered by a great bed apparently about 1,000 feet thick
of black augitic lava, and over this there are at least 5 grand
alternations of such rocks and aqueous sedimentary deposits, amounting in
thickness to several thousand feet. I am quite afraid of the only
conclusion which I can draw from this fact, namely that there must have
been a depression in the surface of the land to that amount. But
neglecting this consideration, it was a most satisfactory support of my
presumption of the Tertiary (I mean by Tertiary, that the shells of the
period were closely allied, or some identical, to those which now live, as
in the lower beds of Patagonia) age of this eastern chain. A great part of
the proof must remain upon my ipse dixit of a mineralogical resemblance
with those beds whose age is known, and the character of which resemblance
is to be subject to infinite variation, passing from one variety to another
by a concretionary structure. I hardly expect you to believe me, when it
is a consequence of this view that granite, which forms peaks of a height
probably of 14,000 feet, has been fluid in the Tertiary period; that strata
of that period are altered by its heat, and are traversed by dykes from the
mass. That these strata have also probably undergone an immense
depression, that they are now inclined at high angles and form regular or
complicated anticlinal lines. To complete the climax and seal your
disbelief, these same sedimentary strata and lavas are traversed by VERY
NUMEROUS, true metallic veins of iron, copper, arsenic, silver and gold,
and these can be traced to the underlying granite. A gold mine has been
worked close to the clump of silicified trees. If when you see my
specimens, sections and account, you should think that there is pretty
strong presumptive evidence of the above facts, it appears very important;
for the structure, and size of this chain will bear comparison with any in
the world, and that this all should have been produced in so very recent a
period is indeed wonderful. In my own mind I am quite convinced of the
reality of this. I can anyhow most conscientiously say that no previously
formed conjecture warped my judgment. As I have described so did I
actually observe the facts. But I will have some mercy and end this most
lengthy account of my geological trip.