RECORD: Darwin, C. R. Geological diary: From old observations I think hills north of Berk S[ound]. (3-4.1834) CUL-DAR34.76-86 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrected and edited by John van Wyhe, corrections by Gordon Chancellor 11.2011. RN2

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text. See the Beagle diary pp. 434-439.

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Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin.

See the introduction to the Geological Diary by Gordon Chancellor.


76

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From old observations I think hills north of Berk S. must run W by N — and hills south of head of do run W 1/2 N

in the outer South of do range, the cleavage. a & therefore probably hills run run WSW & ENE. after crossing the W 1/2 N. parallel ranges there is valley. — (casa de los cones we then come to the great Falkland range of hills; these run W between W by W & W by S. & form as it were a bifurcation with the above range:

The great chain must attain an elevation of above 800 feet. is composed where I have seen of granular quartz rock. — very frequently with small specks of blank imperfectly crystallized mica ( [blank] ) On the South side of this range, the country is low. & undulatory to a most remarkable degree

76 verso

؟ does not the quartz more dip to S by W. (than SSW?). — ∴ agree with slate, more than sandstone:

I use the term elevation with respect to the quartz ranges. as being far most probable:but if the coincidence is very strongly proved between quartz & slate. What shall we say?

77

(2)

The valleys generally run parallel to main chain, but they are intersected in every direction by arms of the sea. —

The rock is generally a coarse blue slate: there is much sandstone; I believe such rocks to form all the southern parts. — I have a specimen from the W end of Eagle Isd brought by the schooner. — the outlying S. islands I believe generally to be coarse quartz rock. — at Cape [Mardilla] It seems universal that in the lower intermediate country between the quartz ranges the rock is essentially a soft slate:

Whatever cause made the great & numerous valleys [might already] the whole mass so as to cause this: —

The above slate. has speaking quite roughly an E & W range of cleavage. —

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78

(3).

In crossing the W by S range of great hills. — I first observed a not uncommon dip of the beds to the North as (in old observ) to the East the South one is universal.

After crossing an irregular band of hills there was much quartz forming lying in horizontal beds & being much broken had a mural appearance. — at the South edge there were some fine instances of the dome stratification: some strata of quartz dipped vertically to the South, the tops of which were arched, so as if continuous would unite with the horizontal lines plans. — The section was like that of half a vaulted passage. — & ran for som & evidently continued for some short distance on southern edge of hill. — f

[sketch]
(S.) little lines represent supposed continuation of horizontal strata: now the surfaces

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(4).

as shown the tops extremities are much cracked & broken: but yet there are complete pure arched strata. 4 or 5 feet long. & 2 or 3 thick with the curvature represented: again the surfaces of the strongly marked planes of division are curvilinear & parallel to the outward form. — Hence there have not been horizontal strata upheaved & arched by an inferior force: (without we suppose a bed of brittle quartz 2 or 3 feet thick can be bent without being cracked.) — but the strata have exactly that appearance which any semi-hardened substance would posses after being subjected to the above sort of force. —

It is a strange coincidence the upheaval & formation of the beds being nearly contemp: !

At the Considering this chain we have a rough anticlinal line [sketch] S N

At the foot of the above hill, I saw another broken arch way. each side being correspondingly arched. & again beyond. this vertical

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[page is missing but there is no break in the material]

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(5)

strata. (which may be supposed to have lost. their arched tops thus forming a second parallel but lesser line of elevation. —

In the western part of the Island this main quartz chain bends up in NW by W & SE by E direction. — I found in the lower part. with that common coincidence. that the cleavage of slate ran in the same direction. — the beds of quartz would point out a still greater change for they dipped to SW by W (∴ ∠ 40° ran NW by N)

In one this place. I noticed, the following fact two crests were seated in the line of dip & almost 20 yards part —

[sketch] SW by W ∠40° A L B

Seeing these strata so close & not every part not seeing past beds one certainly would suppose they were part of one bed & the effect of one elevation

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[sketch]

necessary Structure

20 yard

[sketch]
10 ft

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(6)

But taking this part of the strata into consideration: we must consider there has been lines of curvature for A as well as B. although only 20 yards apart.

Remembering the small doom line at foot of great range: It must be admitted probable that all the numerous crest lines (in old observations) are parallel ones of elevations: although they have a tendency to cast the upper strata more on one side than the other:

After crossing these NW by W hills forming termination of the island - again we come a lower wave-like country of slate. I have found in one plain slate dipping at to SSW. —

There were some quartz hills on my left hand. which I imagine to be a termination of W 1/2 N. ranges

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83

(7).

There is one very curious fact I noticed for 2 or 3 100 yards in the valley. where the quartz hills bifurcate. we have a common blue slate. with the usual dip N 1/2 E. ∠ 50°-60°. with this there were parallel layers of slaty sandstone, which in color & every other character is similar to that near the town. —

these inclined layers of sandstone were tracing by very irregularly horizontal to water lanes of brown iron. —

Now we have seen a slate with the exact usual exact cleavage overlying & under nearly horizontal beds of the same sandstone, so that we have proof that the cleavage was this originally formed in ver t an arched position: here we have proof. that the same power has separated the materials which go to form sandstone & slate

83 verso

X This case is exactly similar to the layers of quartz in gneiss at M. Video — when from another cause I felt sure they must have been formed in their present relative position:

Here water is [illeg]. & I believe them. —

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(8)

& placed them in their present inclined position!. — if I had not seen the same slate with same cleavage overlying & [illeg] horizontal sandstone, I should of course have thought the sandstone slate & alternating sandstone must have been horizontally deposited & tilted into present position. — It seems wonderful that this unknown cleavage power could plain the particle of such a mechanical rock. as the sandstone. — We may remember on the ve beach- leaf sandstone of last coast of Tierra del, there W were some concretionary masses of sandstone.

Now this clearly shows a motion in the particles after deposition: the puzzle is here that the motion must have taken place in a great thickness of bed. I could trace some of the alternating sandstone 9 & 10 feet. — X

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85

(9)

Mr Lyells. theory of many elevations has explained many appearances in Tierra de Fuego. — I think it also alone by allowing the continual action of the sea can explain the excessive number & intricacy of the valleys & present arms of the sea. — which like a medusa's Head. intersecting the land

These latter are not now forming by the quiet (so quiet dead & quiet as to contain scarcely any living animated creatures) & which are now filling up. — But raise the sea 100 feet & you have an efficient cause.

There is another general & curious phenomenon. — viz enormous streams of great blocks of quartz rock.

They occur in valleys from a few to 3 or 400 yards wide; which posses only an inclination of a few degrees; they are deep, as

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86

10

know by the sound of running water: the fragments are nearly angular & of all sizes many very large. — The universal covering of peat is now crawling over these great masses of blocks & clearly concealing them. — They occur high up on the hills as well as low. —

The inclination is so very small in some cases. — that the former which could have rolled great angular blocks as if they had been fluid. must have been excessive. such as perhaps produced by very violent earthquakes. —

If as I am inclined to imagine the lower parts of the island of slate. are only same.

86 verso

[sketch]


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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

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