RECORD: Darwin, C. R. Geological notes made from Capt Fitz Roy Specimens collected on the coast. CUL-DAR37.686-687. Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online,

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections and editing by John van Wyhe 1.2013. An illegible name was supplied by Gordon Chancellor. RN2

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink.

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.


1835 Geological notes made from Capt Fitz Roy Specimens collected on the coast of Peru


3207 ... 3212
At Cobija there is one specimen of a close grained ferruginous imperfect Syenite: we also have dark grey compact stone Porphyritic Lava with white Feldspar. & red harsh, altered stone, which sometimes contains Cryst specks of Carb of Lime. The latter clearly belong to the Porph. Breccia formation: the former is either one of the old subaqueous Lavas or injected rock..— There is much salt on the whole surface. —


3213: 14 At Arica the rock on the beach is an impure stink-stone Lava stone containing black cherty concretions. 3215 — Also a stratified rock which it is very difficult to say exact nature: 3217 I believe a sediment of broken crystals &c are blended by subsequent metamorphic action. — There is also some of the true Plate Porphyry 3216. containing black crystals. —

Here we may suppose at at Iquique. the escarpement of Porph. Breccia. comes close to the Beach. — At Cobija it could not have been far distant. —

686v [blank]




The whole surrounding country by Capt. FitzRoys account is either covered. by a singular rather hard dark brown stone 3218. abounding with salts. on the outer surface of which. pieces project as if in a Breccia. — But on first fracture, it would rather appear to be a Pseudo-Breccia. Such occurs on the high neighbouring hills. On the hard layer of pure semi-transparent salt: which has on its superior surface another soft opake saline substance. 1264 Tin Label — Here we see a close similarity with the alluvial covering of Iquique. The brown stone perhaps corresponds to the concretions in the Tisa. — May we conjecture saliferous sandstone is here present?

This supposition may possibly though throw some light on the very doubtful origin of the salt & nitrate of soda. It would appear that this saline covering extends the whole distance from between Arica to & Cobija (270 miles)

Islay. 3205 3206

At Islay the commonest rock appears very close grained syenitic granitic crystals almost blending together. — & anothe some gneiss. — Whole soil granitic. — In patches, there are layers of white very fine volcanic ashes with black mica & little fragments of Trachyte. —

687 verso

RN p. 102 abstract

Lesson describes grand tertiary form of Payta

Sowerby has shells

Mr Bollaert says seam of Hucilagaya run NE by E & SW by W.

William Bollaert (1807-1876) writer, chemist, geographer, and ethnologist, Bollaert worked as an assayer in the silver-mining province of Tarapac√° and later surveyed for the Peruvian government.

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