RECORD: Darwin, C. R. Geological diary: Dark Harbor. (12.1835) CUL-DAR35.286-287 Transcribed by Kees Rookmaaker, edited by John van Wyhe. (Darwin Online,

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections by John van Wyhe 5.2011. RN1

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Reproduced with permission of the Syndics of Cambridge University Library.


December 28th. [1835] — At Cone Harbor, read all this

Dark Harbor (rocked up now).

Rock all micaceous schists, much & regularly laminated, dipping within a point of WSW. ∠ very various often about 40° have seen it 20° & nearly ┴°

Rock (2437) grey, quartzose micaceous schist: which often containing numerous grains (2441) of quartz & occasional side of silvery mica

To the North of Cone Harbor, form of land perhaps point at considerable extent of the volcanic formation

Ynche Isd December 30th. —

Inqui Island. — N. of N. point of Tres Montes Peninsula all the rock either the same as (2447), a quartzose grey rock with grains of quartz (2442): or it passes into a finer grained variety with semi-conchoidal fracture & which is closely connected (2443) with these feldspatic

Lat: 45.48.

286 verso

X Mem: Granite at Cone Harbor

The age of the rock there are hence unquestionably the same, with the whole of Chonos. Archipel:

؟ Is not the direction of outer coast of P. Tres Montes NNW (true): ∴ // to cleavage? —

Dykes not abundant here or at Dark Harbor, only near seat of volcanic action: & at Midship Isd. —



rock of Cone Harbor, which were described as containing specks of quartz. — The rock here differs from Dark Harbor in form not being laminated but rather divided by numerous smooth extensive planes of fracture, which intersect each other at about angle 45°. — Hence every outlying point is ornamented with numerous fe pyramids. (this is the striking character of the coast & on a great scale perhaps accounts for such hills as the "Cone".

By gradual & perfect mineralogical transition we can trace micaceous slates into the slaty quartzose rock & this again into one which closely corresponds in every respect to what I have called "altered slates", & which the included breccia (at Cone Hill) seem render highly probable. — The dip where they have been ascertained have been similar: It is interesting as showing to what origin mica slate may be attributed. —

287 verso [blank]

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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (

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