More Letters of Charles Darwin Volume II

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I hope you will allude to Mauritius. I think this is the instance on the
largest scale of any known, though imperfectly known.

If I were you I would give up consistency (or, at most, only allude in note
to your old edition) and bring out the Craters of Denudation as a new view,
which it essentially is. You cannot, I think, give it prominence as a
novelty and yet keep to consistency and passages in old editions. I should
grudge this new view being smothered in your address, and should like to
see a separate paper. The one great channel to Santorin and Palma, etc.,
etc., is just like the one main channel being kept open in atolls and
encircling barrier reefs, and on the same principle of water being driven
in through several shallow breaches.

I of course utterly reprobate my wild notion of circular elevation; it is a
satisfaction to me to think that I perceived there was a screw loose in the
old view, and, so far, I think I was of some service to you.

Depend on it, you have for ever smashed, crushed, and abolished craters of
elevation. There must be craters of engulfment, and of explosion (mere
modifications of craters of eruption), but craters of denudation are the
ones which have given rise to all the discussions.

Pray give my best thanks to Lady Lyell for her translation, which was as
clear as daylight to me, including "leglessness."

LETTER 486. TO C. LYELL.

Down [November 20th, 1849].

I remembered the passage in E. de B. [Elie de Beaumont] and have now re-
read it. I have always and do still entirely disbelieve it; in such a
wonderful case he ought to have hammered every inch of rock up to actual
junction; he describes no details of junction, and if I were in your place
I would absolutely dispute the fact of junction (or articulation as he
oddly calls it) on such evidence. I go farther than you; I do not believe
in the world there is or has been a junction between a dike and stream of
lava of exact shape of either (1) or (2) Figure 2].

(Figures 2, 3 and 4.)

If dike gave immediate origin to volcanic vent we should have craters of
[an] elliptic shape [Figure 3]. I believe that when the molten rock in a
dike comes near to the surface, some one two or three points will always
certainly chance to afford an easier passage upward to the actual surface
than along the whole line, and therefore that the dike will be connected
(if the whole were bared and dissected) with the vent by a column or cone
(see my elegant drawing) of lava [Figure 4]. I do not doubt that the dikes
are thus indirectly connected with eruptive vents. E. de B. seems to have
observed many of his T; now without he supposes the whole line of fissure
or dike to have poured out lava (which implies, as above remarked, craters
of an elliptic or almost linear shape) on both sides, how extraordinarily
improbable it is, that there should have been in a single line of section
so many intersections of points eruption; he must, I think, make his
orifices of eruption almost linear or, if not so, astonishingly numerous.
One must refer to what one has seen oneself: do pray, when you go home,
look at the section of a minute cone of eruption at the Galapagos, page 109
(486/1. "Geological Observations on Volcanic Islands." London, 1890, page
238.), which is the most perfect natural dissection of a crater which I
have ever heard of, and the drawing of which you may, I assure you, trust;
here the arching over of the streams as they were poured out over the lip
of the crater was evident, and are now thus seen united to the central
irregular column. Again, at St. Jago I saw some horizontal sections of the
bases of small craters, and the sources or feeders were circular. I really
cannot entertain a doubt that E. de B. is grossly wrong, and that you are
right in your view; but without most distinct evidence I will never admit
that a dike joins on rectangularly to a stream of lava. Your argument
about the perpendicularity of the dike strikes me as good.

The map of Etna, which I have been just looking at, looks like a sudden
falling in, does it not? I am not much surprised at the linear vent in
Santorin (this linear tendency ought to be difficult to a circular-crater-
of-elevation-believer), I think Abich (486/2. "Geologische Beobachtungen
uber die vulkanischen Erscheinungen und Bildungen in Unter- und Mittel-
Italien." Braunschweig, 1841.) describes having seen the same actual thing
forming within the crater of Vesuvius. In such cases what outline do you
give to the upper surface of the lava in the dike connecting them? Surely
it would be very irregular and would send up irregular cones or columns as
in my above splendid drawing.

At the Royal on Friday, after more doubt and misgiving than I almost ever
felt, I voted to recommend Forbes for Royal Medal, and that view was
carried, Sedgwick taking the lead.

I am glad to hear that all your party are pretty well. I know from
experience what you must have gone through. From old age with suffering
death must be to all a happy release. (486/3. This seems to refer to the
death of Sir Charles Lyell's father, which occurred on November 8th, 1849.)

I saw Dan Sharpe the other day, and he told me he had been working at the
mica schist (i.e. not gneiss) in Scotland, and that he was quite convinced
my view was right. You are wrong and a heretic on this point, I know well.

LETTER 487. TO C.H.L. WOODD.
Down, March 4th [1850].

(487/1. The paper was sent in MS., and seems not to have been published.
Mr. Woodd was connected by marriage with Mr. Darwin's cousin, the late Rev.
W. Darwin Fox. It was perhaps in consequence of this that Mr. Darwin
proposed Mr. Woodd for the Geological Society.)

I have read over your paper with attention; but first let me thank you for
your very kind expressions towards myself. I really feel hardly competent
to discuss the questions raised by your paper; I feel the want of
mathematical mechanics. All such problems strike me as awfully
complicated; we do not even know what effect great pressure has on
retarding liquefaction by heat, nor, I apprehend, on expansion. The chief
objection which strikes me is a doubt whether a mass of strata, when
heated, and therefore in some slight degree at least softened, would bow
outwards like a bar of metal. Consider of how many subordinate layers each
great mass would be composed, and the mineralogical changes in any length
of any one stratum: I should have thought that the strata would in every
case have crumpled up, and we know how commonly in metamorphic strata,
which have undergone heat, the subordinate layers are wavy and sinuous,
which has always been attributed to their expansion whilst heated.

Before rocks are dried and quarried, manifold facts show how extremely
flexible they are even when not at all heated. Without the bowing out and
subsequent filling in of the roof of the cavity, if I understand you, there
would be no subsidence. Of course the crumpling up of the strata would
thicken them, and I see with you that this might compress the underlying
fluidified rock, which in its turn might escape by a volcano or raise a
weaker part of the earth's crust; but I am too ignorant to have any opinion
whether force would be easily propagated through a viscid mass like molten
rock; or whether such viscid mass would not act in some degree like sand
and refuse to transmit pressure, as in the old experiment of trying to
burst a piece of paper tied over the end of a tube with a stick, an inch or
two of sand being only interposed. I have always myself felt the greatest
difficulty in believing in waves of heat coming first to this and then to
that quarter of the world: I suspect that heat plays quite a subordinate
part in the upward and downward movements of the earth's crust; though of
course it must swell the strata where first affected. I can understand Sir
J. Herschel's manner of bringing heat to unheated strata--namely, by
covering them up by a mile or so of new strata, and then the heat would
travel into the lower ones. But who can tell what effect this mile or two
of new sedimentary strata would have from mere gravity on the level of the
supporting surface? Of course such considerations do not render less true
that the expansion of the strata by heat would have some effect on the
level of the surface; but they show us how awfully complicated the
phenomenon is. All young geologists have a great turn for speculation; I
have burned my fingers pretty sharply in that way, and am now perhaps
become over-cautious; and feel inclined to cavil at speculation when the
direct and immediate effect of a cause in question cannot be shown. How
neatly you draw your diagrams; I wish you would turn your attention to real
sections of the earth's crust, and then speculate to your heart's content
on them; I can have no doubt that speculative men, with a curb on, make far
the best observers. I sincerely wish I could have made any remarks of more
interest to you, and more directly bearing on your paper; but the subject
strikes me as too difficult and complicated. With every good wish that you
may go on with your geological studies, speculations, and especially
observations...

LETTER 488. TO C. LYELL.
Down, March 24th [1853].

I have often puzzled over Dana's case, in itself and in relation to the
trains of S. American volcanoes of different heights in action at the same
time (page 605, Volume V. "Geological Transactions." (488/1. "On the
Connection of certain Volcanic Phenomena in South America, and on the
Formation of Mountain Chains and Volcanoes, as the Effect of the same Power
by which Continents are Elevated" ("Trans. Geol. Soc." Volume V., page 601,
1840). On page 605 Darwin records instances of the simultaneous activity
after an earthquake of several volcanoes in the Cordillera.)) I can throw
no light on the subject. I presume you remember that Hopkins (488/2. See
"Report on the Geological Theories of Elevation and Earthquakes," by W.
Hopkins, "Brit. Assoc. Rep." 1847, page 34.) in some one (I forget which)
of his papers discusses such cases, and urgently wishes the height of the
fluid lava was known in adjoining volcanoes when in contemporaneous action;
he argues vehemently against (as far as I remember) volcanoes in action of
different heights being connected with one common source of liquefied rock.
If lava was as fluid as water, the case would indeed be hopeless; and I
fancy we should be led to look at the deep-seated rock as solid though
intensely hot, and becoming fluid as soon as a crack lessened the tension
of the super-incumbent strata. But don't you think that viscid lava might
be very slow in communicating its pressure equally in all directions? I
remember thinking strongly that Dana's case within the one crater of
Kilauea proved too much; it really seems monstrous to suppose that the lava
within the same crater is not connected at no very great depth.

When one reflects on (and still better sees) the enormous masses of lava
apparently shot miles high up, like cannon-balls, the force seems out of
all proportion to the mere gravity of the liquefied lava; I should think
that a channel a little straightly or more open would determine the line of
explosion, like the mouth of a cannon compared to the touch-hole. If a
high-pressure boiler was cracked across, no one would think for a moment
that the quantity of water and steam expelled at different points depended
on the less or greater height of the water within the boiler above these
points, but on the size of the crack at these points; and steam and water
might be driven out both at top and bottom. May not a volcano be likened
to a protruding and cracked portion on a vast natural high-pressure boiler,
formed by the surrounding area of country? In fact, I think my simile
would be truer if the difference consisted only in the cracked case of the
boiler being much thicker in some parts than in others, and therefore
having to expel a greater thickness or depth of water in the thicker cracks
or parts--a difference of course absolutely as nothing.

I have seen an old boiler in action, with steam and drops of water spurting
out of some of the rivet-holes. No one would think whether the rivet-holes
passed through a greater or less thickness of iron, or were connected with
the water higher or lower within the boiler, so small would the gravity be
compared with the force of the steam. If the boiler had been not heated,
then of course there would be a great difference whether the rivet-holes
entered the water high or low, so that there was greater or less pressure
of gravity. How to close my volcanic rivet-holes I don't know.

I do not know whether you will understand what I am driving at, and it will
not signify much whether you do or not. I remember in old days (I may
mention the subject as we are on it) often wishing I could get you to look
at continental elevations as THE phenomenon, and volcanic outbursts and
tilting up of mountain chains as connected, but quite secondary, phenomena.
I became deeply impressed with the truth of this view in S. America, and I
do not think you hold it, or if so make it clear: the same explanation,
whatever it may be, which will account for the whole coast of Chili rising,
will and must apply to the volcanic action of the Cordillera, though
modified no doubt by the liquefied rock coming to the surface and reaching
water, and so [being] rendered explosive. To me it appears that this ought
to be borne in mind in your present subject of discussion. I have written
at too great length; and have amused myself if I have done you no good--so
farewell.

LETTER 489. TO C. LYELL.
Down, July 5th [1856].

I am very much obliged for your long letter, which has interested me much;
but before coming to the volcanic cosmogony I must say that I cannot gather
your verdict as judge and jury (and not as advocate) on the continental
extensions of late authors (489/1. See "Life and Letters," II., page 74;
Letter to Lyell, June 25th, 1856: also letters in the sections of the
present work devoted to Evolution and Geographical Distribution.), which I
must grapple with, and which as yet strikes me as quite unphilosophical,
inasmuch as such extensions must be applied to every oceanic island, if to
any one, as to Madeira; and this I cannot admit, seeing that the skeletons,
at least, of our continents are ancient, and seeing the geological nature
of the oceanic islands themselves. Do aid me with your judgment: if I
could honestly admit these great [extensions], they would do me good
service.

With respect to active volcanic areas being rising areas, which looks so
pretty on the coral maps, I have formerly felt "uncomfortable" on exactly
the same grounds with you, viz. maritime position of volcanoes; and still
more from the immense thicknesses of Silurian, etc., volcanic strata, which
thicknesses at first impress the mind with the idea of subsidence. If this
could be proved, the theory would be smashed; but in deep oceans, though
the bottom were rising, great thicknesses of submarine lava might
accumulate. But I found, after writing Coral Book, cases in my notes of
submarine vesicular lava-streams in the upper masses of the Cordillera,
formed, as I believe, during subsidence, which staggered me greatly. With
respect to the maritime position of volcanoes, I have long been coming to
the conclusion that there must be some law causing areas of elevation
(consequently of land) and of subsidence to be parallel (as if balancing
each other) and closely approximate; I think this from the form of
continents with a deep ocean on one side, from coral map, and especially
from conversations with you on immense subsidences of the Carboniferous and
[other] periods, and yet with continued great supply of sediment. If this
be so, such areas, with opposite movements, would probably be separated by
sets of parallel cracks, and would be the seat of volcanoes and tilts, and
consequently volcanoes and mountains would be apt to be maritime; but why
volcanoes should cling to the rising edge of the cracks I cannot
conjecture. That areas with extinct volcanic archipelagoes may subside to
any extent I do not doubt.

Your view of the bottom of Atlantic long sinking with continued volcanic
outbursts and local elevations at Madeira, Canaries, etc., grates (but of
course I do not know how complex the phenomena are which are thus
explained) against my judgment; my general ideas strongly lead me to
believe in elevatory movements being widely extended. One ought, I think,
never to forget that when a volcano is in action we have distinct proof of
an action from within outwards. Nor should we forget, as I believe follows
from Hopkins (489/2. "Researches in Physical Geology," W. Hopkins, "Trans.
Phil. Soc. Cambridge," Volume VI., 1838. See also "Report on the
Geological Theories of Elevation and Earthquakes," W. Hopkins, "Brit.
Assoc. Rep." page 33, 1847 (Oxford meeting).), and as I have insisted in my
Earthquake paper, that volcanoes and mountain chains are mere accidents
resulting from the elevation of an area, and as mountain chains are
generally long, so should I view areas of elevation as generally large.
(489/3. "On the Connexion of certain Volcanic Phenomena in S. America, and
on the Formation of Mountain Chains and Volcanoes, as the Effect of the
same Power by which Continents are Elevated," "Trans. Geol. Soc." Volume
V., page 601, 1840. "Bearing in mind Mr. Hopkins' demonstration, if there
be considerable elevation there must be fissures, and, if fissures, almost
certainly unequal upheaval, or subsequent sinking down, the argument may be
finally thus put: mountain chains are the effects of continental
elevations; continental elevations and the eruptive force of volcanoes are
due to one great motive, now in progressive action..." (loc. cit., page
629).)

Your old original view that great oceans must be sinking areas, from there
being causes making land and yet there being little land, has always struck
me till lately as very good. But in some degree this starts from the
assumption that within periods of which we know anything there was either a
continent in such areas, or at least a sea-bottom of not extreme depth.

LETTER 490. TO C. LYELL.
King's Head Hotel, Sandown, Isle of Wight, July 18th [1858].

I write merely to thank you for the abstract of the Etna paper. (490/1.
"On the Structure of Lavas which have Consolidated on Steep Slopes, with
Remarks on the Mode of Origin of Mount Etna and on the Theory of 'Craters
of Elevation,'" by C. Lyell, "Phil. Trans. R. Soc." Volume CXLVIII., page
703, 1859.) It seems to me a very grand contribution to our volcanic
knowledge. Certainly I never expected to see E. de B.'s [Elie de Beaumont]
theory of slopes so completely upset. He must have picked out favourable
cases for measurement. And such an array of facts he gives! You have
scotched, and will see die, I now think, the Crater of Elevation theory.
But what vitality there is in a plausible theory! (490/2. The rest of
this letter is published in "Life and Letters," II., page 129.)

LETTER 491. TO C. LYELL.
Down, November 25th [1860].

I have endeavoured to think over your discussion, but not with much
success. You will have to lay down, I think, very clearly, what foundation
you argue from--four parts (which seems to me exceedingly moderate on your
part) of Europe being now at rest, with one part undergoing movement. How
it is, that from this you can argue that the one part which is now moving
will have rested since the commencement of the Glacial period in the
proportion of four to one, I do not pretend to see with any clearness; but
does not your argument rest on the assumption that within a given period,
say two or three million years, the whole of Europe necessarily has to
undergo movement? This may be probable or not so, but it seems to me that
you must explain the foundation of your argument from space to time, which
at first, to me was very far from obvious. I can, of course, see that if
you can make out your argument satisfactorily to yourself and others it
would be most valuable. I can imagine some one saying that it is not fair
to argue that the great plains of Europe and the mountainous districts of
Scotland and Wales have been at all subjected to the same laws of movement.
Looking to the whole world, it has been my opinion, from the very size of
the continents and oceans, and especially from the enormous ranges of so
many mountain-chains (resulting from cracks which follow from vast areas of
elevation, as Hopkins argues (491/1. See "Report on the Geological
Theories of Elevation and Earthquakes." by William Hopkins. "Brit. Assoc.
Rep." 1847, pages 33-92; also the Anniversary Address to the Geological
Society by W. Hopkins in 1852 ("Quart. Journ. Geol. Soc." Volume VIII.); in
this Address, pages lxviii et seq.) reference is made to the theory of
elevation which rests on the supposition "of the simultaneous action of an
upheaving force at every point of the area over which the phenomena of
elevation preserve a certain character of continuity...The elevated
mass...becomes stretched, and is ultimately torn and fissured in those
directions in which the tendency thus to tear is greatest...It is thus that
the complex phenomena of elevation become referable to a general and simple
mechanical cause...")) and from other reasons, it has been my opinion that,
as a general rule, very large portions of the world have been
simultaneously affected by elevation or subsidence. I can see that this
does not apply so strongly to broken Europe, any more than to the Malay
Archipelago. Yet, had I been asked, I should have said that probably
nearly the whole of Europe was subjected during the Glacial period to
periods of elevation and of subsidence. It does not seem to me so certain
that the kinds of partial movement which we now see going on show us the
kind of movement which Europe has been subjected to since the commencement
of the Glacial period. These notions are at least possible, and would they
not vitiate your argument? Do you not rest on the belief that, as
Scandinavia and some few other parts are now rising, and a few others
sinking, and the remainder at rest, so it has been since the commencement
of the Glacial period? With my notions I should require this to be made
pretty probable before I could put much confidence in your calculations.
You have probably thought this all over, but I give you the reflections
which come across me, supposing for the moment that you took the
proportions of space at rest and in movement as plainly applicable to time.
I have no doubt that you have sufficient evidence that, at the commencement
of the Glacial period, the land in Scotland, Wales, etc., stood as high or
higher than at present, but I forget the proofs.

Having burnt my own fingers so consumedly with the Wealden, I am fearful
for you, but I well know how infinitely more cautious, prudent, and
far-seeing you are than I am; but for heaven's sake take care of your
fingers; to burn them severely, as I have done, is very unpleasant.

Your 2 1/2 feet for a century of elevation seems a very handsome allowance.
can D. Forbes really show the great elevation of Chili? I am astounded at
it, and I took some pains on the point.

I do not pretend to say that you may not be right to judge of the past
movements of Europe by those now and recently going on, yet it somehow
grates against my judgment,--perhaps only against my prejudices.

As a change from elevation to subsidence implies some great subterranean or
cosmical change, one may surely calculate on long intervals of rest
between. Though, if the cause of the change be ever proved to be
astronomical, even this might be doubtful.

P.S.--I do not know whether I have made clear what I think probable, or at
least possible: viz., that the greater part of Europe has at times been
elevated in some degree equably; at other times it has all subsided
equably; and at other times might all have been stationary; and at other
times it has been subjected to various unequal movements, up and down, as
at present.

LETTER 492. TO C. LYELL.
Down, December 4th [1860].

It certainly seems to me safer to rely solely on the slowness of
ascertained up-and-down movement. But you could argue length of probable
time before the movement became reversed, as in your letter. And might you
not add that over the whole world it would probably be admitted that a
larger area is NOW at rest than in movement? and this I think would be a
tolerably good reason for supposing long intervals of rest. You might even
adduce Europe, only guarding yourself by saying that possibly (I will not
say probably, though my prejudices would lead me to say so) Europe may at
times have gone up and down all together. I forget whether in a former
letter you made a strong point of upward movement being always interrupted
by long periods of rest. After writing to you, out of curiosity I glanced
at the early chapters in my "Geology of South America," and the areas of
elevation on the E. and W. coasts are so vast, and proofs of many
successive periods of rest so striking, that the evidence becomes to my
mind striking. With regard to the astronomical causes of change: in
ancient days in the "Beagle" when I reflected on the repeated great
oscillations of level on the very same area, and when I looked at the
symmetry of mountain chains over such vast spaces, I used to conclude that
the day would come when the slow change of form in the semi-fluid matter
beneath the crust would be found to be the cause of volcanic action, and of
all changes of level. And the late discussion in the "Athenaeum" (492/1.
"On the Change of Climate in Different Regions of the Earth." Letters from
Sir Henry James, Col. R.E., "Athenaeum," August 25th, 1860, page 256;
September 15th, page 355; September 29th, page 415; October 13th, page 483.
Also letter from J. Beete Jukes, Local Director of the Geological Survey of
Ireland, loc. cit., September 8th, page 322; October 6th, page 451.), by
Sir H. James (though his letter seemed to me mighty poor, and what Jukes
wrote good), reminded me of this notion. In case astronomical agencies
should ever be proved or rendered probable, I imagine, as in nutation or
precession, that an upward movement or protrusion of fluidified matter
below might be immediately followed by movement of an opposite nature.
This is all that I meant.