RECORD: Darwin, C. R. Geological diary: Port St Andrew - Cape Harbor. (12.1834) CUL-DAR35.259-266 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/).

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections and editing by John van Wyhe, corrections by Gordon Chancellor 5-8.2011. RN4

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

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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.


259

December 21st Sunday [1834]

Port St Andrew Cone Harbor. — Pen. of Tres Montes. —

Island in front: the prevailing rock brownish smoke-grey, rather earthy, greenstone porphyritic with indistinct crystals of feldspar (2382) & green spots. — is traversed by numerous veins, which blend into the adjoining rock of a pure grained much greener (chloritic) greenstone (2383)

There is some[pseudo]-breccia fragments conrection? slided together, altered in their nature most [indefinitely] porphyritic (2384). correction? — The surface is exceedingly rough by small projection, from unequal weathering, apparently the chloritic mineral giving way & from the brecciated structure. — Base of island composed of enormous fragments; the main rock being much traversed by fissures. —

The above rock form a massive support, as seen on both hands in entering in the vessel to a rock dipping about W by N ∠45°, with even & numerous

259 verso

Vultur aura. excessively abundant here. 3 fingered island & Port Otway

no animals, sea-birds & otters seals [refuse] of sea. —

Penguin demersa no nest eggs under in holes under the tussocks or bushes

Barking bird, (large like Junco — mostly brown reddish about abdomen) —Cheucau & Creeper & lastly little black wren (every one nows birds) Humming bird & T. del. Thrush not uncommon & last the common black [Furnarius] on coast in great numbers. (Humming bird in dense forest).1

Wonderful to see kelp on the very outside coast. — degradation of rocks. —

Ascended, cone dreadful walking, curious immense rock. ascended on ladder. saw Hoppner Sound: curiosity to know whether fellow brethren. bit of wood & mans nest. — How strange, a ship-wrecked man! — In the North barren level hills.

1 These ornithological notes are also found in Zoology notes, p. 279.

Penguin demersa no nest eggs under in holes under the tussocks or bushes] in pencil

260

2

planes of of cleavage, yet the rock is itself massive in its structure:

I cannot question it is altered slate such as we have seen in Woollaston Isd. & Cockburn channel. — External forms exceedingly like the mountains of that group: many steep & regular lines & obtusely angular ridges giving architectural appearance to the hills. — Elevation 1500 to 2000 ft.

Going up the harbor: found some of the massive (2385) laminated rock ┴° N by W & S by E is fine-grained grey. Feldspathic (perhaps is a fine-grained greenstone): Found this on two sites & between them nay fragments & one piece mass in situ, of granite mica (or hornblende) with white feldspar & yellowish quartz. Connection? —

The surface of cliffs of 1st variety of rock looks like lava with included fragments, owing possibly I do not know whether to the green veins or really brecciated structure. —

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Monday 22d

The certainly common rock is the feldspathic [alter] slate as yesterday evening (s not clay-slate near trap dyke like this in T del Fuego (2386). This passes in some places by insensible degrees to a slate colored feldspathic with specks of quartz & occasionally porph: with feldspar; sonorous conch: fracture.

When I approached the cone describe it about 1600 ft high, I made sure to find, as well crystallized greenstone; it was however the same kind of rock cliffs, but blacker some black (2387) & less altered; parts were paler & obscurely brecciated structure (2388). This mass certainly appears to be pushed up through the [whole] strata: what could have caused this singular form. Has it a same not melted. Breccia highest part The hills run & creek of waters) NW by 1/2 N & E by S: they are very irregular, but certainly the N & S line of cleavage corresponds to none. —

An old beach of shells about 30 ft above h. water marks (& bed of pebble) also a single fissurable at 200 ft? How came it there?

Mem. granite metamorphic argument W // N dip disturbed

origin of mica slate  [good] proofs &c

Breccia same dip

+ Mem. … dip] in pencil.

261

Tuesday 23d [1834] Cone Harbor. — (3)

The Southern Headland. — On landing (when we returned) was much surprised to find all the rocks volcanic: R

The commonest varieties were brown cellular, rather stony lava (2390: 91) cavities often with green powder coating: less commonly grey ones with similar structure, some of which are of little specific gravity from extreme cellular nature (2392: 93: 94). There is also much of a slate color, so very strong, that excepting from occasional crystal or cellular would not be easily recognized as volcanic rock (2395) as in this latter state: this variety is often laminated (2396), the plates showing a tendency to a globular structure. — Perhaps even a still more kind is a rubby sort which seems related to the pitch stone kind.

This sort frequently from the outer layers of the stone imperfect sphaere of the stony sort kind. — The [illeg] nearly the whole hill side is so much broken up & [illeg] in the nature Line Nearly the whole of the lava is of that nature, that it is very difficult to say, whether it is composed of fragments united by fire or water: the latter can often be proved. I found a mass of angular blocks of the cellular lava, but cemented together, or rather the interstices filled by an entire aqueous deposit; above this were beds of sandstone (2401; 02) brownish, fine-grained, indurated (volcanic debris, containing occasional fragments of lava. this alternated with scores of layers of smally brecciated soft rock, where the pieces appeared pumice (2403). — The sandstone contains numerous little bits of signite, most of which are black & glistening. — The layers are parallel & denote clearly tranquil aqueous deposition; above these beds

261 verso

(a) Lava (2390) is often amygdaloid with agate. I found one great hollow sphere a foot across: the same surface is largely mamillated & red (2400). — The junction of it with the lava is rather curious (2399). —

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Cone Harbor 4

There was great bed stream of cellular lava. — All these beds dipped to about North ∠45. — immediately in front & under their basset edge, there runs what a great dyke of a brownish compact greenstone (2390). This at its very edges becomes slightly cellular & finer grained so as to become somewhat like (2391). On the The rocks possessed a slightly transverse prismatic structure. — On the opposite side of the ravine there appeared (I could not reach it) a corresponding mass of cemented fragments of cellular lava. —

The dyke ran WNW & ESE. it is cer tolerably certain the protrusion of this caused the northerly high dip, in an overlying mass of scorice & sediment. Is this a common occurrence: in the true greenstone dyke it is not often present to be seen: Here perhaps a less pressure would cause the strata to yield with greater readiness. —

In another locality a little further north I found a layer of lava, dipping at great angle (70°?) to the S. — This dar at the foot of some high cliffs, which were built of all the varieties of lava:

They were traversed by what appeared somewhat like a dyke of the variety of (2390): the cells were however exceedingly (lens shaped) flattened & their longer diameter arranged parallel to the dyke; on the other hand, against the dyke like appearance, each side appeared like an aqueous deposit: if this was the case, the dyke must have been a horizontal stream & their present position shows a disturbance on a scale, which I should hardly expect. — Will not the flo direction of cells, answer this question? I do not know on which side this arguments tilts.

The rocks especially the common rubby sort in this cliff were traversed in every direction by layer &

262 verso [blank]

263

Cone Harbor (5

& patches of white friable lime. This must have been contemporaneous with its flowing. — A blow made white powder start out in all parts. — The puzzle, whether masses of solid lava were connected together by aqueous cement or passed by a strong decomposed lava into each other often occurred. —

Mr Johnstone1 brought me from another headland as a specimen of white cellular calcareous tufa penetrated by small veins (2404): & tells me there was some conglomerate. — I could see this same formation was is several hundred feet thick: the form of the land, spoke nothing, a mere weatherworn undulating hill, covered as usual with forest. — I may however remark that some few miles to the South I saw a larger patch of greenish stone soft with rounded outline; which seems connected with a high rounded- hill mountain; I was at the time surprised at its appearance & now feel sure it was is a quaint volcano; perhaps the origin of these streams. —

We may draw following conclusions; that this the lava is subaqueous lava: that the volcano has formed part of an outlying chain of igneous action of which Chiloe is part (Indeed the structure of the lava in the two plains is not very dissimilar). That these volcanoes have caused the above N & S lines of projecting land. —

The relation of this, little suspected, volcanic formation, with the slates of the inner parts of harbor I cannot tell. Who can say the brown porphyritic greenstone which underlies them is different from that of the dyke, which traverses the scoriae & sediment?

If so this igneous volcanic action has metamorphized the slates (it is well

1 Charles Richardson Johnson Mate on the Beagle, see Narrative 2, "Mr Johnstone" is mentioned twice in the Beagle diary pp. 60, 207.

263 verso

(a) The porphyritic greenstone near is not cellular; this however only shows amount of pressure. — [illeg] In both cases a concretionary structure is sometimes shown by a dividing greenish stone, this is the only mineralogical alliance I am aware of. —

(b) Mem: the great plates of fusible lime, which I believe at St Jago certainly flowed with lava

264

Cone Harbor 6

that in Wollaston Isd the rocks of which have already been adduced as similar also possesses apparent volcanic formation). Yet I do not incline to this opinion. — The metamorphis of the slates appears a too general action in all parts of the Andes to be owing to detached volcanoes; it occurs, also as in the Campana, where was is not one. — Who can reconcile the N & S lines of cleavage; the E & W great WNW & ESE dykes; the NW by N & SE by S line of hills? The similarity of cleavage with the St Is the The hills & dykes, being both transverse to cleavage is similar to what occurred at Midship Isd. In both cases are not the dykes fo the true [illeg] places of different ages?

With respect to age of this volcano, I have no data; aspect of the sedimentary strata conveyed no idea of great antiquity. —

The upheaval of good broard belts, certainly 20 yards of strata, by the injection of dykes, at fist appeared so novel to me, that I was rather inclined to consider a line of elevation. I do not however otherwise, than I have described understand the structure & mineralogical nature of the apparent dyke. —

At St Jago we saw that, the whole volcanic district is traversed by veins:

265

Cone Harbor (7)

I examined to day between the altered slates & yesterdays volcano. the rock is all volcanic, & gi almost universally in a solid field structure partly globular — concretionary. — Specimens (2405:) 6: 7: 8: 9) — the first is compact & most abundant; (2408) passes into (2409), the both are quite compact: (2407) seems very similar to (2384) described as occurring between the igneous rocks & metamorphic slates. — Seeing the compact structure, the fickleness of precise mineralogical nature of these rocks & (the short distance 1/2 a mile) to the I felt convinced it was impossible to separate these rocks, from the green one (2382), which seems to have uplifted the slates. — I was therefore surprised to find that the above varieties, quietly passed into a fragmentary mass, which contains highly cellular pieces & were cemented by an aqueous deposit. — Much of these must have actually flowed. — I do not however mean to say that the greenstone (2382) has been a lava stream, but that it is part of the formation possibly fluid mass which probably had not been poured forth or pressure removed.

There was a cliff of about 12 feet of many sedimentary layers, capped by bed of little cellular lave like (2405). These dipped to the NNW ∠ 22°. Close before & almost parallel, there was an irregular dyke running NW 1/2 W & SE 1/2 E, which sent off branches, & cut through both aqueous & igneous rocks, ([sketch] dyke NW 1/2 W), so that in this case the dyke could not have upheaved the NNW strata, but possibly some other branch beneath it must have done so. — These lava fields are chiefly remarkable by the number & size of dykes, & variety in their mineralogical structure. — They are all exactly parallel to each other, & the extremes within 1/2 a mile of each in a line transverse to their direction. — Their sides are generally straight. — There were I counted 7 or 8: — Two Three of composed of the

265 verso [blank]

266

Cone Harbor (8)

fine grained greenstone (2411), one was 10 yd, another 8, another 2. —

[a section of the page was excised, possibly a sketch]

<> immense dyke 20 30 yards wide

<>ike another part of the firled (2406) There were three large

<> - There was a pass, or

<> traversing to common direction

<>ated structure (2410). - These

<>re in a large as nearly to

<>t. I was at first impressed with the idea, that the field was merely the coast of a single stream of lava, fissured & filled up with the inferior & more fluid stone. — But the alternation of numerous fine sedimentary layers (which could only have been deposited in tranquil water precludes this idea.

Surely this bay must have been very near the former volcanic forms, else how can we understand the number & extent of veins. It also better allows for part of the rocks to have flowed & part not. — It is impossible not to be struck with the parallel lines NW 1/2 W or of dyke & the irregular chain of hills NW by W only differing 1.1/2 point. — Seeing how little mineralogical differences can be depended upon, I presume these dykes & those in Midship Isd are nearly contemporaneous. —

I still think, that the slates probably were not metamorphized during the emission of the above volcanic rocks. — the presence of granite bears me out. —

It is very interesting seeing the close connection of the matted mass, which has [burnt out through] uplifted the metamorphosed slates & the true cellular volcanic streams. In this case, the volcano has burst through altered slates & granite. — How do we reconcile the NW & SE line of dykes, here & NE & SW lines at Midship Isd. with the parallelism

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of the volcanic actions to the Andes, which might be expected & which the trend of the land points out. —

The dykes were flowing long posterior to the flowing of lava & aqueous deposits, & contemporaneous probably with the formation of mountain chain. the line of volcanoes owing perhaps to cleavage & long anterior. (NB. Almost always the mineralogical nature of dykes is different from the beds they traverse.)

(Age of dykes


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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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