RECORD: Darwin, C. R. Geological diary: First of Chonos Islands (Midship Bay). CUL-DAR35.272-273 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)
REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections by John van Wyhe 5.2011. RN1
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.
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Reproduced with permission of the Syndics of Cambridge University Library and William Huxley Darwin.
See the introduction to the Geological Diary by Gordon Chancellor.
December 16th.  — (1)
First of Chonos Islands. — (Midship Bay.)
Micaceous schist 92378: 79). — consisting of convoluted layers of quartz
with divided by thick seam of micaceous phyllade after becoming ampellite. — The quartz is exceedingly abundant in large layers. we may imagine the two minerals of common mica slate are here each collected into separate layers. The common dip was to within 1/2 point of SW (compass) ∠40°:
I saw it vertical where the dip was more southerly. — The schist is crossed by numerous dykes. I found former extensive ones, composed of massive pale-grey granular (2380: 81) greenstone. containing few crystals of feldspar: little iron pyrites &
( grains of quartz ) if this latter mineral is present we may imagine greenstone proceeds from fused micaceous schist:
The two main dykes had a direction of NE & SW (by compass) the others between NE & N by E: one was 9 yards broard,
other 7, 3 & 4th 1 to 2 yards wide. They had been
Mem: good sized, but not healthy trees of T.del. Beech
immense quantity of Cryptogam: plants
At S. Pedro Torres a little deer & mice
This very small expand [illeg]
Deer on Lemuy on C. Tres Montes
Where plain no trees, but thick peat formed by Big Plant (specimen of white flowers with tufts of common grass & sea plant & little stunted Beeches. latter trees 1/5 of wood
No arborescent grasses: T del Fuego creeper
Lat: 45° 18'
(Decembr 18th went to see)
Lampyrus [illeg] genus Iselaphus & Staphylinus & Cynus abundant in the forest & cryptogamic flora
broken by many faults, at nearly rt ∠r to their course. — There were lines of fracture parallel to the dyke: &
brok the dykes necessarily crossed the laminae of slate at high angles: ( argument against [illeg]
All these dykes were within 1/3 mile of each other. — All the greenstone were similar, hence from some subterranean mass, hence coeval. — the faults must have been caused by a slipping of the schist in direction of laminae. — a drawing or stretching in same direction as caused the crack of dykes would confirm this. —
The hills & creeks in the mica slate islets & forms of many parallel to cleavage viz. NNW (true). —
Mem: not on S. Pedro
Height of main mountain run to E
SE NE & W &E? (V. chart when completed)???
Porphyry of the nature of dykes??
The height of the main range must be
about between 2 & 3000 ft: one peak being 2900 ft
[December] 20th. [Sailed] to North. — Noon — (Tres Montes). — Weather beach coast lofty — steep like W. [Alanter] Island. —
remarkable number of trees on windward side, [illeg] abrupt points. — dangerous
Altered slate running NNW & SSE?? Many cones greenstone
On coast South of Cove Harbor, judging from the ship. —
Funarius like water wagtail
There can be little doubt from external appearance, that the main range is composed of granite, as that near Patch Cove North part of C. Tres Montes.
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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)
File last updated 2 July, 2012