RECORD: Darwin, C. R. Geological diary: Fernando Noronha. (2.1832) CUL-DAR32.39-40 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 5.2010, further corrections by Gordon Chancellor, corrected against the manuscript by van Wyhe 7.2010 . 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.
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Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin.
1832 Feb. 20th Fernando Noronha (230 miles from C. St. Roque) 26
As far as I was enabled to observe during the seven hours I was on this island, its geological formation appears very uniform. — Fernando really consists of several small islands. — but they may be considered as one in as far as relates to their Natural History. The extreme length is about 9 miles & 3 in breadth. — The most remarkable feature is a
lifting a peak hill on the north end of the main island. — Tot height is about 1000 feet. — the base is not very steep & thickly wooded, but the peak whether seen at a distance or near is of a most singular appearance. — it is about 400 feet high. & shaped irregularly conical. The southern side overhangs. the others are nearly perpendicular:
255...258 Phonolite Humboldt? (
Petro siliceous? Leucostini Dec: Class: Trachyte. Daubeny
The rock of which
it the whole hill is composed consists of numerous crystals of villous feldspar & a few acicular ones of hornblende in a greenish feldspathic base. — it is brittle, very sonorous, & divided into columns. — Whilst viewing the group of Islands from the highest accessible point. viz. the base of the peak. — other cones are seen. of a less height. but doubt certainly of the same formation. — Immediately on seeing them. one is inclined to attribute their origin to mass of rocks partially softened by heath & protruded from beneath. —
[in margin, position unclear] Dr Webster in the Chanticleer Voyage1 says the peak is composed of a greenstone of felspar, quartz & Hornblende; the quartz the great component part! embedded masses of siliceous schist: surely glossy felspar is mistaken for quartz !! & this writer criticises Playfair & other geologist. —
The coast near the Town. presents a type of the lower parts of the island. — Here
1 Webster 1834, vol. 2, p. 327.
(a) This cleavage appears to be owing to scales of vitreous feldspar arranged in the same planes.
(b) The Phonolite occurs on each side of the mass of Tufa & its accompanying basaltic dykes. — As these dykes are of ordinary appearance I suppose are of course injected from
below an inferior mass of basalt. — Therefore the Basalt Phonolite alternates (& is superior (?)) to the Basalt — which is in direct opposition to what Humboldt says more is the case. — (This is a mere conjecture). —
(c) The rock & soil being much the same I was
much surprised at the much greater fertility of this island compared to St. Jago. — I should conceive this latter island to be (as it now exists) of a much later origin than Fernando & therefore the soil rocks are not so much decomposed. but I chiefly attribute the difference of to the prevailing winds at the two places. At St Jago the NE trade blows during the whole year & coming off the coast of Africa must be very dry; at Fernando the prevailing wind is SE & of course passing over so large a track of ocean must be loaded with moisture. — In a Tropical country, where rain does not fall for so many months the state of the air must have a most considerable effect on the vegetation.
I should conceive from the appearances of the rocks that the island owes its origin to about the same period as central parts of St. Jago. — The projections are reversed in St Jago. the Basaltic far preponderate. in Fernando the Trachyte — in both, the latter is in conical projecting masses
1832 Feb. 20th Fernando Noronha 27
is seen the same Feldspathic rock, although in places it has a slaty structure 259 & 260, cleaving in direction NW. —
With Near this, there occur large beds of white Tufa (a), through which numerous dykes run. varying in thickness from 8 feet to a few inches. —
Mem. Dr Webster says there is limestone ∴ ? tufa?
These are composed of two rocks; one black basalt amygdaloidal with carb: & Lime & containing numerous crystals of Augite 261...263; the other with a white & coarser base slightly vesicular containing minute vitreous crystalline feldspar & Augite 264. — This latter also occurs in beds. — In this part of the coast, numerous large blocks of basalt (with olivine?) are scattered 265...268. it is quite evident that they come from above. — & at a distance in another part I saw a black mass of columns, in all probability of same nature. — (b)
The pebbles on the coast are cemented together. — The whole island is covered with trees, & from a height looks like one single wood, with a few spots cleared for cultivation. — The soil which results from the decomposition (c) of the Feldspathic rock is a pale clay.
with containing unaltered crystals. although exceedingly dry, it appears to be very favourable to vegetation. — On the hills Leechens & mosses covered the rocks. & I there remarked a grass. — I could not help being surprised at the almost entire absence rarity of monocotyledonous
[in margin] Dr Webster says Isld not volcanic because no scoriae. Overlooks amygdaloidal dykes! forget that scoriae could be remote.
1832 Feb. 20th Fernando Noronha 28
plants, excepting those cultivated by the inhabitants. — Large
masses of the columnar rock shaded by laurels & ornament[ed] by a leafless
tree covered with fine pink flowers like Dystachis, only of more [delicate]
colour, gave to the nearer parts of the scenery a beautiful effect. — &
the bright sight of a tropical scene could not fail to render the more distant
islands & wild outline of the coast exceedingly striking. — The woo[ds]
were full of birds, but not of many sorts. — doves & a bird. like the
english willow wren were very common: I was surprised to see Terns settling
on the trees in flocks. — Both
boobys noddys & a most graceful
little tern of a snow-white colour when disturbed from the branches, hovered
in great numbers round our heads. like little angels — I did not observe any
hawks or ravens; which is curious. considering the number of birds that would
serve for prey. & the secure building place the rocks would afford. them:
compared to St Jago it is quite inexplicable.
How can birds of preys catch others in a Wood?!
Mice & Lizards are in great profusion, as I believe is always the case in a hot dry country. — The commonest animal is a little ant. — which builds a nest often 3 feet high & 2 thick, round the stems of trees. It is formed of tough dark brown substance & is full of irregular cavities, disposed without any order. — from the bottom a broard covered way goes to the ground, & from the top small ones branch off along the boughs of the tree. —
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