RECORD: Darwin, C. R. Geological diary: Brazil coast. [8.1836] CUL-DAR32.1-2 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)
REVISION HISTORY: Transcribed from the microfilm by Kees Rookmaaker, corrections and editing by John van Wyhe 4.2010, corrected against the manuscript by van Wyhe 7.2010. RN3
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.
Brazil coast (32.(1))
Baron. Roussin. —1
The coast N. of St Thomas (60 miles N. of C. Frio) is all low as compared to the part extending to St. Catherines
mention general soundings.
I have mentioned
Proceedings northwards from Bahia the coast is generally low.
— I have mentioned shells in Limestone at R. S. Francisco. — At Alagoas. There
is no hard rock, so that the ballast of ships is eagerly sought for. — At
Pernambuco, the low sandy
banks land on which the town is situated,
is surrounded at a distance by a semicircle of hills, or rather by the edge
of a bank country, elevated perhaps 200 ft above the sea: — I only
had an opportunity of examining these at one place at Olinda. There a reddish
cliff was composed of coarse par siliceous particles, very slightly
aggregated, embedding. very numerous pebbles of white quartz. (a) —
(a) spotted with clayed matter
The mass might almost be called gravel. — Parts were glittering white, others
red the colours being irregularly mottled; the
super whole is horizontally
stratified; the superior strata are redder & more aluminous. In the midst
of the sand & pebbles: both layers & detached concretionary irregular
masses of a quite white, or pale purple clay occur. — 3880:81 It is fine,
soft & greasy to the touch, adheres to tongue, contains minute scales
of mica & atoms of quartz. — The formation bore the
(a) spotted with clayed matter] added pencil.
stamp of originating from the disintegration of granitic rocks. — At the base of these hills, & skirting the low swampy land, there are some fine grained yellow Limestone rocks. —
These are very impure, being either sandy. aluminous or ferruginous; the stone is totally
cor hard: it is associated with yellow clay: I could observe no embedded shells; but there are irregular cavities, which somewhat resemble the casts of vegetable matter. — I do not know whether these calcareous rocks pass under the sands & conglomerates, or merely face them. — I believe from what I heard, that the higher land in the neighbourhood, is all constituted of the granite sand such as that of Olinda. — There is an evident connection between this formation & the superficial one overlying the gneiss at Bahia. — I do not doubt. but to similar parent rocks occur likewise here, at some distance in the interior. —
North of Pernambuco,
for the whole space
N B. The remarkable facts respecting the reefs will be mentioned in the coral paper.
to the mouths of the Maranhao the coast is exceedingly low. — it is probable hard rock occurs in very few parts. — at C. Blanco, the cliffs are said by Roussin to be composed of white sand, which probably belongs to the same formation. — In the northern parts of this coast, there are extensive trails, desert & covered with dunes of white sand. —
Read Humboldt first volumes geology of Venezuela.1
Near the mouth of Maranhao, clothed with green mangroves. —
Orbicular granite Daubuisson p. 3082
Read Humboldt first volumes geology of Venezuela.] added pencil.
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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 22 March, 2013