RECORD: Darwin, C. R. Geological diary: Quail Island. (1.1832) CUL-DAR32.15-20 Transcribed by Kees Rookmaaker, edited by John van Wyhe. (Darwin Online, http://darwin-online.org.uk/).
REVISION HISTORY: Transcribed from microfilm by Kees Rookmaaker, corrections and editing by John van Wyhe 5.2010, 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. Where pencil was used instead this is noted in the textual notes. 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.
1832 1) Jan 17 & 18 Quail Island. — St. Jago
Quail island a small desolate spot lying
S close to Porto
Praya. — Its shape is oval from N. to S barely a mile in circumference. There
are round Porto Praya several truncate conical hills: this island may be considered
one of the set. .but with sea instead of a sandy valley at its foot. — The
washing of the sea round its base affords a good section & I thought by
studying the island attentively I might find a good keystone for the neighbouring
Hill on which town stands is a kind of Isld
(Begin at Page 7)
I will begin by the lowest beds & describe the whole succession with minuteness. — Before however doing this I will give a general outline, of what appears to be the formation of the island. —
The foundation consists of volcanic rocks, which formerly were the coast of a sea: the line runs through the island, & in the section on each side, we have a large bed of sand & gravel, full of broken shells, which gradually lessens in thickness. till it ides away: it has the exact appearance, as if a piece of the present beach was lifted up & cut off. — Overlying both this sand & the part of volcanic rock, which the former sea had not reached to me have a solid mass of antient lava. — after this the whole mass of beds to be upheaved to the present [site]. to the West & over the bay, the white line of raised coast. dividing the 2 masses of black volcanic rock is seen
See the woodcut of Quail Island from Volcanic islands, p. .
Hill on which town stands is a kind of Isld] added pencil.
stretching away for many miles. —
(A) The lowest rocks all contain included crystals the most common is (1) Augite & Olivine (?) there are masses of (2) amygdaloidal, containing in cavities minute white crystals: Many of these rocks have undergone great (3) decomposition in parts becoming either a yellow, red or green clay. including the unaltered crystals of augite: these are all mingled & interlaced with great confusion: in other parts there are (4) dykes of a harder rock, which stand. out. from better resisting the weather. these rocks assumes a transverse columnar form: & from
Total height of cliff above high water mark is 44 feet. — the line of white sand is 30. — ∴ covering of Feldspathic rock is 14 feet thick. —
Mr Sulivan1 makes the highest part of Sandstone on Quail Isld 38 ft. — Highest part of island 50 ft. And the lava is not quite so high above the sea.
Mr Sulivan made white line in cliff head of Anchorage in one part 59 ft in another 61. — This line is rather below half of the cliff ∴ height about 40 ft. Where however the third stream has capped the top the height probably 180 ft. —
(5) (77-81) & (
1 Bartholemew James Sulivan (1810-1890), second Lieutenant on the Beagle.
Mr Sulivan...180 ft. —] added pencil.
A. Lower crystalline rocks
C. Beach of former coast
D. The common covering of Lava. vesicular. —
E. Bed of pebbles left by the torrent that cut through the rock
F. Posterior current of compact Lava form Flag Staff Hill. —
The 2 F° are separated about 1/2 a mile. —
The dykes about 150 yards across
X [(1836)] present line of valley from form of melted lava.
[D (1836)] is frequently divided into two streams
sketch across the entire page in pencil, only the letter labels are in ink.
Highest part — 55. 4 feet
Observatory — 49. 3
North Bluff — 47. 1
Bluff over sandstone 50. 0 (27)
Highest part of sandstone 38. 6
Another measurement 40
Highest part... 38. 6] all but the pencil additions are not in Darwin's handwriting.
Quail Isld] added pencil.
Another measurement 40] added pencil.
N. B. all the beds dip in the direction of the diagonal line: so that the upper covering of Lavas becomes much thicker in S end of the Island
sketch in pencil across the entire page, only the lettering and 'Level of Sea' are in ink.
Level of Sea
1832 Quail Island
(2 Jan. 17 & 18
(1) Nos: (52-58) & (64-69)
(3) (58 & 59. 68. 69)
(2). the white crystals effervesce with Mur. Acid
the cracks of such higher parts. being filled with sand. I should think they must be of contemporaneous origin. — The line of former sea. coast crosses the Island. NE & SW. & the sea washed the southern parts of island & therefore, as might be expected, it is at the north end. that we see these inferior volcanic rocks. in the greatest thickness. — they here show a section of about 20 feet. — to the south they are hidden by increasing thickness of the deposits from the sea. & the natural inclination of a beach. —
I will now describe the beds of this coast. beginning at the lowest or southern end of island: the higher.
the we mount of course they extend further round the island. B The lowest (5) bed is of more surely indurated character than the other & contains a remarkable number of Turritella. & some few other shells. Patella &c &c
(2) (17-21) (27-34)
(3) (25 & 26)
Effervesces readily with Mur: Acid. gives precipitate with Oxalate of Ammonia. Under Blowpipes becomes slowly caustic. & with Nit. Cobalt remains of a Violet colour. — Carbonate of Magnesia. (?) Carb of Lime
(1) The organic remains in these beds are certainly of a Tropical type. & as far as my knowledge goes. are the same as those of present day. —
I should think this old coast. one of no great duration? —
1832 3 Jan. 17 & 18 Quail Island
Several alternations of coarse gravel. large rounded stones, & fine sand. — this contains a great variety of shells. — Cardium. Voluta a (1) rugged Astrea in great profusion & adhering to the rocks on which they lived: patellae in vast numbers. — Littoral shells carried outwards
This is best seen on Eastern side of Island. & here 12 or 18 feet thick. on the West it is only a foot: on this side the gravel is cemented into a very hard conglomerate but as this process is now going on on the coast of island. perhaps it may be the work of the present day. —
D This is a bed of very various characters generally it is white
or grey sand. (2) almost entirely formed of minute shells & corallines.
— The lower part of this is very remarkable. by being. almost composed of
(3) concretionary masses of a white mineral: frequently being pisiform
& having nucleus of some other rock:
up this & inferior beds
often have the appearance of a wall built without mortar: The upper (4) parts
of this & in near contact with superior Feldspathic rock become very hard:
it is then white spotted with yellow. — At the South of island, the sand is
cemented into a fine (5) sandstone. —
Examine these specimens with care.
In these beds. besides numerous small shells I found crabs & perfect bones of
a Echini. — (1)
E Above these beds. as far as they extend & upon the Crystalline rocks (A) there is a horizontal
Littoral shells carried outwards] added pencil in margin.
Examine these specimens with care.] added pencil.
(1) In places this rock has entangled & fixed portions of lower augitic rock. —
(2) The Eastern side of island is much more regular
(a) (12-15)(& 71)
(c) 72 & 73
(3) By this fault a small portion of grey sand or extremity of shore has been carried down
1832 Quail Island 4 Jan. 17 & 18
cap of a hard (a) feldspathic rock. which has the appearance of Basalt: in some parts it has the appearance of plains of stratification. & in other of 5 sided columns. occasionally curved. — About a foot of the lower part is (b) carious & harsh. — The (6) upper is slightly so. & in parts is divided into large
concentionary concentric balls. — 3 feet in diameter: giving a tessellated appearance to the rock. — (1) This formation varies from 6 to 20 feet in thickness. —
The general height of Island is about 40 feet. but the beds on it often vary this relative height. in parts the grey sand is 30 feet above waters edge. in others close to it: (2) this is chiefly owing to dislocation of which there is a very marked one at (K) (K) (3). —
Upon the whole I should think it
clear probable that after the marine beds were had been quietly deposited on the inferior roc Volcanic rocks. a sheet of melted matter (E) was spread over them: that the whole mass was then raised. since which or at the time there has been a partial sinking. — I judge of this from the appearance of distortion. & indeed. the distant line of coast seen to the East. which is considerably higher bears me out. —
(a) 35 & 75
(b) 36 & 76
(b). Slightly effervesces with Mur. Acid. & under blowpipe gives a white coast — it then easily melts into black enamel. — In the places. where the lower crystalline rocks are much decomposed I observed the pebbles in the sea. coated with mud: is it not this that again uni[tes] & forms the hard matrix? does not
to its action under blowpipe render it probable? Can the Carbon which effervesces. be Magnesia? & does not Magnes. harden under water? —
1832 5 Jan. 17 & 18. Quail Island 5
The cap of rock which crowns the island. appear to be a part of a large sheet. — this I think both from its own appearance (1) & the distant contour of above mentioned truncate conical hills:
(1) the edge are angular all round the island
it remains perfectly inexplicable to me the cause of these isolated patches: the long continued action of water is here precluded. by the presence of shells of modern date. —
There is now going on a very remarkable process. on the coast of this island: viz the formation of an extremely hard (a) conglomerate. — This in the northern end overlaps the volcanic at the southern. the former sea-coast. — The conglomerate is formed both of the lower Crystalline & upper feldspathic rocks & is cemented together
in by a black tough (b) matrix. — I could have scarcely credited. that rocks nearly as hard as the conglomerates of older formation (viz. of red-sandstone formation Anglesey) could daily be increasing under my own eyes. — My proof is 2 bolts or large nails of Iron. & Bricks So firmly imbedded that I could by no means detach one of them. — How inexplicable some of here appearances here seen would have been. if they were on a larger scale. —
This present formation includes shells. So that probably we might have had an apparent bed of
& Bricks] added pencil.
[19 verso blank]
1832 Jan. 17th & 18th — [small sketch] Quail Island
recent shells. placed between two of a more remote origin. —
I have not mentioned a small covering of diluvium on the western side of the Island. — At first. I thought it merely debris from the upper feldspathic rock. — but on examining I found numerous fragments of the lower augitic rocks. — it does not appear to be of marine origin. although it is the most probable explanation. — It looks to me like a part of the long disputed Diluvium. —
N. B. This account was written. before I had examined any part of St. Jago. — & the first words I ever wrote on this subject. All my views have remained much the same. — Excepting that. the place at North end of Quail Island
instead of being where the line of crust terminates. instead of being the mainland, was an island in those antient days. — This is clear from finding the former beach to the north. under Praya & it has been described as seen in all other sides.
I have drawn my pen through those parts which appear absurd. —
& the first words I ever wrote on this subject] added pencil.
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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)
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