RECORD: Darwin, C. R. Geological diary: Chiloe. June-July. 1834. CUL-DAR34.201-205 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 4.2011. 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 the permission of the Syndics of Cambridge University Library and William Huxley Darwin.

See the introduction to the Geological Diary by Gordon Chancellor.


201

Following The promontory on which the town stands: we first have a strange mass of vast angular fragments of various volcanic rocks (chiefly compact A) these are firmly cemented together: a little further we meet with (A) compact variety itself, some of the exterior layers are curvilinear; the great mass of angular fragments which occur & tilt in many place on the coast clearly overlie, directly the Lava or Basalt. — in some places this Breccia is so mingled with the lava, that I think it must have been involved in the lava. — The lava affects an angular cleavage, its surface is cellular. — it is occasionally truly vesicular (F). — at other times amygdaloid with lime. — As I have said, the common variety is the very compact sort (A). — Varieties passing into Pitchstone (B) (C) are nearly as abundant. —

(B) (C) (D) occurred close together, & passed into each other. — There is a red porphyritic kind (E). — which is found close to a black basalt with crystals of white feldspar. — Then other, pale colored less crystalline varieties (G). — But the most remarkable is the

201 verso [blank]

202

frequent passage of the hardest basalts into more or less pale clays or wackes. — Now these changes are not very gradual. — the basalt is at point of contact rather softer, & the wackes contains nodules of harder rock. The wacke shows a porphyritic structure. — Where a concretionary structure is present in the basalt it is found in the wacke. — Now these changes (H) take place apparently without any sort of order. —

transition lateral

masses of lava occur in the midst of the wacke & projects up at at different heights. — Hence from weathering during the upheaval of the land, abrupt masses stand out on the coast. — the connection of which with the surrounding land, at first much puzzled me. — Perhaps the wacke more commonly overlies the hard rock. —

I am do not know on what this lava lies, therefore its age is doubtful. — I have seen a bed of round volcanic pebbles separating two masses therefore there would seem to have been two currents; both superior & inferior was much mingled with great fragments. —

Above the lava in many places or more commonly the wacke

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203

(3)

there is a stratified substance, closely resembling wacke, abr & evidently resulting from its abrasion interstratified with blackish, laminated clay slate & a fine breccia. — This is covered by a thin bed of shingle of older rocks. — I have no doubt these beds correspond to those about Cheverea's creek. where to where the lava has not extended. — Fragments of volcanic rocks almost render it certain. —

I should have stated that the field of lava is difficult to be traced, perhaps this is owing to the weathering away of the wacke. — the wacke not having crystallized, cannot be owing to any difference in heat. —

In many places, a great mass of grey. hardened mud with small fragments overlies the field of lava

I should think perhaps poured out with lava. — the want of cleanliness & clearness of edges. Great contrast with S.Cruz lava. —

I found many small caves at about 8 12 10 feet

203 verso

[Huaso] Isd half slate! —

204

above water, in one of which there was much grey sand, with fragments of shells & cuts exactly like beach. — [sketch] structure of cavern. — Capt Williams. says about 4 feet. land has risen or water fallen during the last four years. — Knows by building a vessel.

Earthquake during this time not known to be coincident. —

Earthquake of Valparaiso not felt here no or v.versâ. — (Ashes fell in town from Osorno.) — Yet coast rising, some more general law. (Earthquake felt as far south as. [Isd of Wager]) —

I should previous to last 12 feet rise ground for many years stationary. —

[sketch] argument about pebbles retiring beaches

form of country

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205

5

On the beach facing the ship, we have a variety of volcanic rocks & fragmentary masses: some of the varieties have large nodules of Carb of lime. V (Ks) —

I may notice that with respect to the fragmentary masses, it is impossible to point out any line, where the mass was formed & united by melted lava & where the water alone has been this agent. — I found the lava overlying beds of black clay slate, yellowish clay, & fine breccia, which alternates in horizontal layers. — they precisely resembled what we have seen overlying the lava, in a short space these layers passed into a fragmentary mass. —

A pitchstone bed overlies a horizontal bed of wacke. —

On the road to Castro, all the rocks are volcanic, generally in the upper part a grey, laminated var earthy variety is present. —

I should have hardly known this excepting by its congeners with some crystalline vesicular rocks. hence we see lava at the higest part of this island: it was covered by vein of bright yellow clay (resulting from the wacke) & a cemented shingle of Cordilleras rocks. —

The coal mine, on the point, consists solely of rounded masses of the above butiminous matter, cordilleras pebbles & volcanic do. cemented in recent breccia; hence there must be a bed at bottom of the ocean: on a great fragmentary mass there are vertical tortuous veins of foliaceous carbinaceous mass; —

From description I think there must be a crater near Castro in centre of Island. — Reexamine wacke beneath pitchstone — At Castro beds of shells. — (Some say limestone on coast). — Superstitious bell rock. — Indian graves. —

The point of Chiloe, which forms the straits, contains some true disintegrated granite. — saw specimen

205 verso

Excellent coal of Estacillos & at some island in the archipelago

[205 verso]

Chiloe.

June-July. 1834


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