RECORD: Darwin, C. R. Geological diary: Observations on the bottom of the sea between the Falkland Islands & St. Cruz. (4.1834-1.1835) CUL-DAR34.87-92 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 3.2011. 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.


87

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April 1834. Observations on the Bottom of the sea between the Falkland Islands & St. Cruz

(The lead. brings up every thing in a circle, diameter of which 2 & 1/2 inches. —)

The First soundings, obtained after entirely leaving the Falkland group were at noon in Lat. 50°.2'. Long. 63°.25'. Distance from nearest part of coast of Pat: 195 miles. — — depth 85. Fathoms:

The bottom was apparently a mottled sand, but really was composed of very minute. 1/80th to 1/100th of inch rounded fragments of black & reddish rocks & transparent quartz. it appeared to part in bed of sand. — These some four 40 miles to the Westward examined where they were rather larger. — & will be described

With the lead there came up a fragment of Echinus (perhaps allied to Cidaris. large pointed striated spines & smaller ones of dark red color. — I should not be surprised if it should eventually be proved this tube (Mem. Echina & Echinus in 57 + 50 Fathoms coast of Patagonia) was commonly even the Encrinitus in the other series, are supposed to be inhabitants of great depths. —

In the noon of the next day (11th)

87 verso

Scattered remarks

40 miles NE of C. Virgins in 50 Fathoms piece of an Echinus was brought up. —

Abreast of Gallegos, out at sea. 57 fathoms fragment of Pecten & Ophiusmis

I observe sounding from 40 to 60 fathoms on coast of S. Patagonia the bottom chiefly consists of small pieces of Balanidae.

Between Staten land & Falklands in 50-70 fathoms consisted of small stony corallines. minute fragments of shells. Spirotis. —

Porph. Pebbles Falkland Land off Staten lond
Dec. 17th. Lat 43°.30' S. the water seems in shade perpendicularly stay very pale blue, was of a remarkable colour: "Venditer blue" with tinge of green & milk. — Depth 55 fathom sandy bottom. — In the ensuing year Decemb 16th in same place — sky cloudy — remarked very same peculiar color.

Speculation R N p 97, p. 98

"Martin white on soundings in Channel"

Beechey on [illeg] R.N. Yankee edition R.N. p. 971

Compare transport of gravel from Cordilleras to Alp or Wales

Roussin in soundings R.N. p. 912

1 References to the Red notebook, p. 97 etc. Beechey 1832.

2 Red notebook, p. 91: 'B. Roussin states that generally in North part of Brazil. <gravel becomes> sand less & gravel more common. the shoaler the water & nearer the Banks'. Roussin 1826-7.

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examined, & found them precisely the same as the great Porphyry pebble bed of Patagonia: the rust-yellow peculiar sort of St Julians Porph: was present; the black ones was when broken of chiefly dark reds (& some obscure green) all more or less Fusible in blowpipe:

there were some jet black also fusible. — I think both here & for the rest of distance the quartz became less present, as perhaps might be expected from increasing distance from the Falklands, its probable origin. —

75: Lat 49°. 40'. Long 65°.4'. —

To the noon of the 13th to Santa Cruz we ran about 130 miles. therefore soundings are further apart. —

62: — Now the last was 75. & before it 65: 64: Here there is a depression 66 feet lower than one side & 72 than other. — Can it be caused by centre of tidal stream between Falklands & patagonia? (Say 65 to 40) less than 1/10th 62. 56: 55: 44 with pebbles about 1/12th of inch): (38 pebbles nearly 2/10" long)

25; 23: about 11 miles from the shore. pebbles 3/10 or 4/10 long: 19: 17: about 6 or 7 miles from shore. —

pebbles about as large as nuts: 12: 11: 3 or 4 miles from shore. pebbles as large as walnuts ∴ yje bottom here apparently[viz] indurated clay. for there was no impression of the holes of Pholandes: —

The distance between just two places where we had 85. fathoms & 17, is 113 miles: the fifference is 45 (or 270 feet) fathoms, which gives an inclination or dip of 1°..22". —

88 verso

Beechey

R.N. p. 45 Beecheys change in soundings on NW coast

Mr Martin states facts about nature of soundings changing near coast — within 25 fathoms come bottom. He says it may be seen in Nories chart — all chart of channel —

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The tides are on this coast very powerful (give example) the rise being about 40 feet all along the coast even off the [illeg] the Beagle fell (& [illeg] enters) although doubtless the main stream. of tide runs N & S. I was much surprised at finding at the distance only of 15 miles pebbles only about 0.4 of inch large. — And these form so great a bed of shingle as the Patagonian one. — Very minute ones are as we have seen present at 195 miles. — From the same cause I was surprised at not meeting with fragments of littoral shells, as muscles & limpets whcih so abound in the coasts.

The following fact would seem to prove that even at trifling depths the water has little power over even small pebbles. — Outside of the bay & completely exposed & about 3 miles from shore in 10 fathoms water when tide rises & falls 40 feet pebbles of various series, some not with greater diameter than 1/2 of inch, were encrusted with species of Flustraceae, which were living & producing eggs: one [of] these had the cells provided with most delicate stony setae, barely visible to the naked eye: the whole surface of the bottom was closely striated with thin pebbles (there were very many soundings taken). now it is impossible to suppose these are ever agitated one against the other, else the Corallines. encrusting convex surfaces, could not retain their setae. — These pebbles were not protected by in hollows or behind large blocks, for the lead would have showed either of these cases. —

89 verso

(z) the depth taken from mean level of sea : some came from rather deeper water

The pebbles & corallines form specimen (1947)

It may be added that besides the great rise & fall of tide, a powerful river enters in front of where the pebbles were found, which one would imagine would increase force of currents. —

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The weight of pebbles & diameter of setae ought to be maintained.

This coast certainly is a weather one.

But several miles off Staten land from in 50 to 60 fathoms water porphyry pebbles supported many delicate & growing corallines. the plain is notorious for its currents. Tide-pips & gales & turbulent sea. —

May 12th

When we sailed from S. Cruz in a SW line to look for the L. Aigle rock. — I attended carefully to the soundings. — There was the same general absence of large pebbles; the bottom consisting of sand & very minute shingle from the Patagonian bed. the same general scarceness of organic remains. —

In 48 fathoms not far from the coast, pebbles with many corallines were procured. specimen (2008). —

In 87 fathoms I found one spine of some Echinus.

Lat: 01°.48': Long: 64°.50' When [blank] miles from the Falkland Isld I noticed a great increase in quantity of quartz granules. —

At anchor off C. Virgins I first saw large. indi pebbles indisputably from T.del Fuego. — Standing immediately to the south, a submarine continuation of the St of Magellan, the water deepens suddenly to between 40 & 50 fathoms & the bottom is composed of slate & quartz pebbles from rather smaller & larger than 1/2 of an inch in diameter. — with occasional larger ones. —

90 verso

Nature of Soundings in the Narrows? —

Mr Kent1 gave me a semi-rounded pebble. from 1 1/2 square 1/2 inch deep. brought up in 27 fathoms near Tea Island (west end of W Falkland) a place remarkable for swell & strong current. This pebble was encrusted on all sides by delicate & encrusting corallines. — They are now rubbed by manner of conveyance but probably they were originally quite perfect. — Specimen 2324. —

1 William Kent, Assistant Surgeon on the Beagle, 1833-1836.

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To the North & South of this channel, the soundings on the banks the soundings are much finer. —

The depth of the water in the narrows where Capt. King states the tide sometimes to run 9 (?) knots an hour is about 40 fathoms, the bottom is of shingle. —

I noticed off the mouth of the Straits, that in the space of a few miles, the nature of the bottom would differ remarkably; we should have mud, with pebbles, pebbles, minute shingle & fine sand. —

With respect to the movement of substances in very deep water, it there is an indisputable proof that such does occur viz: the shoaling in the mouths of all the inlets on West coast of T. del Fuego, when within there may be no bottom with 1000 feet; these materials must have been heaped up. — (or caused by greater degradation near the coast line of violence?)

91 verso

Decemb. 27th. 1834. Sounding a few miles from coast of C Tres Montes (turbulent sea): 32 fathoms, sand in small pebbles, oblong. greater diameter 2/8th breadth 1/8th: also in 40 fathoms (further from shore) coarse sand, equal grain with diameters about of 1/40th to 1/50th of inch. —

Stone presented by Capt. Beaufort to Geolog. Soc. from 80 fath South of Cape Horn encrusted with corallines

Le Peyrouse vol III (1) p. 417.1 50-60 bottoms leagues from land that of Japan passage to Formosa 45 fathoms

1 Dillon 1829.

92

Playfair P 4141 gives an excellent account of the Progress of pebbles by his system of lifting up & down, the corallines might adhere; — anyhow it is a proof of greatness of this remnant, the bottom of deap sea, still & deep dark But the rounding of the subaqueous stones attributed to same cause cannot well happen. —

One of the quartz pebbles from the Falkland Isle is rather complex sepc (2322)

؟ The pebbles encrusted on all sides?

The depth of soft mud [tested] by Playfair of [Mulgrave] will well account for great band of concretions at S Cruz

Particulars of Capt Ross's deep soundings? —

App Jan 6th 1835 Approaching Chonos Archipel: fine sand from 40 to 20 f (becoming coarser). 18. fath. small pebble: 16 f. quartz pebble quite clean. 9 x 8 diameter rounded depressed

7th Jan 1835 Chonos Archipelago
40 fathoms pebbles 1/2 " in diameter: 65 f angular bits of hardened clay — 1/4 of m

corallines was brought up: oval (. 1.5 x 1.1) depth .5. — 3 & 4 miles from shore. — Jany 1835

In the Inland sea (76 fathoms) East of Chiloe. corallines & bit of a Pecten (spec 2526)

1 Playfair 1802, p. 415. The same reference was recorded in Darwin's Santiago notebook, p. 118 and in CUL-DAR32.146 verso.

92 verso [blank]


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