RECORD: Darwin, C. R. Geological diary: St Mathias Bay / St Josephs [Bay]. [4.1833] CUL-DAR34.7-9 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online,

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. 311-312.

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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.


April 17th

St Mathias bay. near entrance of St Josephs: a natural section of the cliffs which runs W by N & E by S, show numerous lines of stratification which are exceedingly regular & parallel to each other. — thet at first seemed horizontal but it was evident there was a small dip to the East: that in lines which some miles to the westwards were some feet above the present sea. approached close it in the East. — This is what would happen in the present day; as we [invariably] find the bottom very gradually deepens from same to the East — have successive deposits on so gentle an inclination would dip to the East: For a distance of 20 miles there was a grand division in the cliffs in the upper part, unto between the lower & the blacker upper stratified beds. — these filled up inequalities in the lower: is it not the gravel described in St Josephs bay. — At entrance of St Josephs bay

7 verso

the cliffs seem to rent on horizontal strata of white rock: =

From the very regularity of East dip — & perfect parallelism. it is evident these beds have not been upheaved: — the cliffs are about 60 feet high — to form the crystalline sulp of Lime. — the water must have been deep to have been literally undisturbed.

I found very similar, if not identical coralls growing abundantly in 30 fathom (or 180 feet).

The ocean then in all probability has subsided about 250 feet: Circumstances have not gone on gradually. — water bearing gravel (hitherto only mud) has cut up the lower beds. — & make a change in animated nature. did the water subside suddenly or gradually? It remained whilst the upper beds of very modern shells was were formed. The there the remains of a succession beaches from gradual retirement, on the bottom of the sea: — the arth looks not sandy enough: yet Patellas. Mytilus give some cause of suspicion for former hypothesis. — Naturem in terroga: —


April 18th

The outer cliffs of the

The cliffs on the outside bankof the entrance into St. Josephs bay are about 60 or 70 feet high. —

The lowe bed about 1/2 of ehole is formed of a compact earthy earth & about 1/5 of its weight is composed of shells. — There are chiefly enormous Ostreas: & various (a) species of Pectens also few univalve allied to Turritella: also on Pecten a Balanus & a Coralline. above this another bed more stratified & softer. & (b) rather lighter coloured & seems to contain few or no shells: in this are horizontal layers, but sometimes curved of crystalline transparent sulp: of Lime Selenite — the laminae are at the crystals layer: Curious occurrence layer about [no number] inches thick.

8 verso

Above this a bed 2 or 3 feet thick of small round pebbles, chiefly jaspers (K), (or [illeg] rocks stained with iron) & concretions &c: also porphyries: — above this is more earthy bed.

(K) chiefly porphyries: black compact horny base with small crystals of porph felspar & other minerals & mica.

Above this an earthy bed. contains layers of quite different shells.— (c) chiefly Patella. Buccanum. Mytilus. & a sort of Balanus. — there were evidently of a much more [illeg] appearance; & as far as I could judge resemble those now found in Falkland Islands: there were also fragments of shells from lower beds:

These upper shells (as far as


I could judge in 5 minute different from those now lying on the beach: by the action of the weather, then these sorts are mingled on the beach: what confusion for future geologists: —

Is the line of pebbles the long black line? The pebbles resembled those at M: Hermoso: There is said to be skeleton of whole & corals in these cliffs: cliffs rapidly wearing away: —

[sketch] modern shells pebbles crystal X X shells
though beach of above pebbles

thus weathering by the sea in flat projected table: —

9 verso

The shells & abundant corallines were confusedly placed in the Earth. — I am surprised they could flourish so well in water which deposited contained so much mud: beds of great thickness

(a) the Earth is here more arenaceous & (from abrasion of shells?) contain Carb of Lime. —

The great oysters are perforated by Chona celata (& by a Pholas?) marked with dendritic manganese: several coralline. some Flustra; Retepora very abundant & coralline allied to one I called Celleporania & others. — These seem all to resemblethose found near Tierra del Fuego coast in about 20 fathoms:

also a Caryophillia: The shells did not blacken or emit smell in flame

(b) much much more aluminous & finer grained. much carb of lime:

(c) These shells blackened & emitted smell in fire on Mytilus encrusting corallina with paps: retained its blue colour & a Balanus a faint red. — the patella had lost its: In all probability these species now exist but from different locations not on this beach: How gradually suddenly has a perfect change in the shells taken place: a bed of gravel only separates them:

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