RECORD: Darwin, C. R. Geological diary: Tierra del Fuego (appendix). (2.1834) CUL-DAR32.96-97 Transcribed by Kees Rookmaaker, edited by John van Wyhe. (Darwin Online, http://darwin-online.org.uk/).

REVISION HISTORY: Transcribed from microfilm by Kees Rookmaaker, corrections and edited by John van Wyhe against the manuscript 7.2010. RN2

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Where pencil was used instead this is noted in the textual notes. 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.


96

1834 Feb Tierra del Fuego Appendix (79)

Wollaston Isd

I add these notes made during this visit, at to those of P79. because the rocks seem to have most connection. — In neither case do I understand their nature. — The present situation is about 10 miles to the SE of Sunday bay. — The commonest rock is a blackish green 1866 & 1867. very little crystalline amphibolic one & which seems to partake in many of the characters of slate. — Externally however it is divided on a larger scale by numerous. smooth planes of divisions. — Another common variety is the same rock. appearing to contain fragments of slate (as in Feldspathic rock in Navarin Isd). — The surface, produced by weathering 1868 produces the resemblance of a breccia in a very strong degree. — At the foot of a hill which will be described. there is rock similar (1866.) also one occurring with red crystals (1869) 1869, in which a Greenstone occurs in globular concretions 1870. it contains pyrites; & merely forms a mass in the other rocks. — Ascending one of the loftiest of the rugged hills, we have at the base rock like (1866) divided by numerous planes of into great shoals. — the most abundant plane dipped at ∠ 18° to S 1/2 E. — We There is also much of the Breccia — like rock; In the higher parts this becomes less frequent; there is however a variegated pale yellowish feldspathic rock 1854 penetrated & blending with what resembles a blank slate? On the rough broken ridge, a fine grained, more

97A

[printed map:]

Chart of a Part of South America.

Surveyed by order of
the Rt. Honble the Lords Commissioners
of the Admiralty under the Direction of Capt. P.P. King R.N.
During the Years 1826-30.

Purple

Purple] added in pencil in Darwin's handwriting. There appear to be traces of watercolour added to the coast near Port Desire.

97

(79

1834 Feb T. del Fuego

Wollaston Isd

crystalline amphibolic rock (1853) 1853 1855. it occurs with variegated sort & with globular connection of a black, sonorous fine-grained amphibolic rock with a conchoidal fracture. — These three rocks are traversed by irregular vein like masses composed of several minerals 1859 ... 1865, of which garnets are the most abundant. & some of which appear curious. — The very peaks are chiefly composed of a porphyry. 1856 1857 of amphibolic rock with white opake feldspar crystals, with this is the variety (1853). — In these rocks there were some small quartz veins! —

The porphyry is traversed (a) by vertical smooth planes which run in N 27° W & S 27° E line & in which there are low crests. — The chief ridges however run in a W 3° N & E 3° S. line; thus intersecting each other at an angle of 60°. — strata obscure cleavage place of colsum & harshness

But this cannot be of general occurrence, for the island is composed of the most rough & jagged peaks, which are very steep, & in the circular valleys there are lakes. — Are these more crystalline peaks the lower rocks (1866 ... 68) altered by heat & are not these latter, also transfigured slate?? The feldspathic rocks in Sunday Bay is accompanied by slate. —

I may here mention, that with respect to the conglomerate P90 found in this Island, containing red scoriae &c &c if as perhaps it probably it should be pronounced to be volcanic. yet it must owe its origin be of from to very ancient one, V oth. side

strata…hardeness] added pencil.

97 verso

volcano, one in which the regular cone, crater & streams of lava have been worn away. — I think this. because I have now seen all the East side & formerly very nearly all of the West & Southern parts & amongst such strongly marked peaks a volcano could not fail to be seen. —

(a) In the Porphyry there were also planes of alteration of color & hardness & division which dipped at small angle to the S.


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