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(A) Many scattered notices accounts have appeared of dust which has fallen in considerable quantities on vessels off the N W. coast of Africa. It has appeared to me desirable to collect these accounts together, more especially since M. Professor Ehrenberg's has made the remarkable discovery that this dust consists chiefly of Infusoria. I have found ten eleven distinct statements of dust having fallen &; & several of these, extending over refer to a period of more than one day. The chief area, in which the phænomenon has been chiefly observed is in the neighbourhood of the Cape Verd Archipelago. (B) The furthest point northward in which it Dust has been observed noticed to fall, was on board the Prussian ship Princess Louisa* to fall in Lat 10 ° . 29 ' N. & northward & according to Lieut Arlett*(2) states that the water is discoloured, owing in part to the falling of dust, for a long distance both Northward & southward of Cape Noon in Lat: 28°. 45' N.; so that the phænomenon has been observed over a space of at least 1100 1500 miles in latitude. This dust has several times fallen on vessels when between 300 & 600 hundred miles from the coast of Africa: it fell on the Princess Louisa*(3) when (in Lat 14°. 21' N & Long 35°. 24' W.) at the 1030 miles from Cape Verd, the nearest point of the continent. In this case the dust probably cape came from a somewhat greater distance; for it is well known that the country changes from dry to low & wooded about southward the mouth of the Senegal.) II in any case, when the direction

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(A)

An account of the fine dust, which has often fallen s several times on vessels, off the N. W coast of Africa. by Charles Darwin M.A. F.R.S

(Used)

(B) Alter

The furthest point southward is which I have met with recorded (is) by Mr Burnett*(1) in Lat 4°. 20' N: Northward, according to

Capt. Hayward in 2.5.6'

(Mr Fletcher Please do not leave any margin) Alter all the [Margins] (area will be greater.)

(Used)

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Baron Roussin states that his survey

(The dust is of a pale reddish-brown colour; it fuses under the blowpipe easily into a dark (grey or black) bead, under the blowpipe : it is generally excessively fine, & adheres to the sails & every other object on board. When the Beagle was ten miles off St. Jago (with the wind from the coast of Africa & the visible horizon only about a mile distant) I found a considerable quantity adhering to the under side of the horizontal wind-vane; & which it appeared to have been filtered from the air by the gauze, when as the ship lay inclined to the wind: Lieut. James*4 *3 collected over four successive days on four successive days consi four packets of the dust on four (which, together with a written communication I owe to the kindness of Mr Lyell [illeg] (but he despaired of being able to do so, until he moistened by causing it moistening a thought of moistening a sponge, washing it & filtering the water washing it & filtering the water. Near the coast continent the dust appears to fall in large quantities: Baron Roussin*4 states that his survey was impeded by the thick fog or haze, "that prevails almost all the year" in Several vessels have been ship-wrecked from owing to this cause*(5) ; & Horsburgh (*5) recommends vessels all ships, to avoid the passage between the Cape Verd Isld & the mainland, from the haziness of the atmosphere

When During the days three weeks we remained at St. Jago, in the Beagle, the Astronomical instruments were found to be injured by the almost constantly falling fine dust. Near South & North of Cape-Noon, Lieut Arlett describes the water as so discoloured, & as thick that the track of a ship is visible for a long time, & he attributes this in chief part to the fine sand blown from the deserts, "with which

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of the wind is mentioned, during a fall of dust, it indicates that the it has been blown from the

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everything on board soon became perfectly caked."

[Arlett, W. 1836. Survey of some of the Canary Islands, and of part of the western coast of Africa in 1835. Journal of the Royal Geographical Society of London 6: 285-310. Darwin's abstract is here.]

Other authors *6 (7) describe the discoloration of the water further southwards at some distance from the coast further southward. From several statements (*7 8) it appears that even the dust which falls on vessels, even when at the distance of many hundred miles from the land, is considerable in quantity, & that the atmosphere is thus rendered by it quite hazy.)

According to Roussin According to Roussin as long as the wind keeps parallel to the shore, the haze & dust extends only to a short distance, but when the harmatten rises prevails from the N.E. & E.N.E, during during the months of January, February, March & even April, from the NE & ENE, the dust is spread through the atmosphere, & stars & other objects are hidden when below thirty degrees from the horizon. Dust, however, was blown on Lieut James' vessel, when between 400 300 & 500 miles from the land by a SE & E.S.E wind; & it was blown, as late as on the 8th of May 8th on the Princess Louisa, when a thousand miles from the sh continent: in many all the other recorded case of dust being having been blown to a great distance, it has occurred within the four above specifyed months.

The dust is not always of the same character: Lieut. James states in his M.S. account, that on the 6th of March on the when in Lat 21°. 40' N Long: 22°. 14; W 280 300 miles from the land, a thick haze came on, with SE wind & that on the

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next morning (when in Lat. 21°: 40' N. & Long: 22°: 14' W and 330 miles from the land) the deck was covered with fine sand.

This sand consists of irregular, angular, transparent, variously coloured particles of about the 1/1000 of an inch square, mingled with some few larger particles & many much finer : smaller: it melts with difficulty into a gray bead.

On the three succeeding days, the ship sailing obliquely from the land, dust of a very much finer character like that which I collected off S. Jago continued to fall. (A) With the wind from the SE & ESE, the distance from the land was only a little less on the 7th than on the succeeding days; so that we must suppose, that the coarser particles were carried borne along by the sudden commencement of a squall, or strong breeze which began had begun by a squall, in which had subsided into a moderate breeze by the time it had reached the ship. The sudden circumstance of a squall or strong breeze which later became gentle. The circumstances of particles of stone, above the 1/1000 of an inch square, being carried nearly at least 350 miles by the wind is interesting, as showing how much further the smaller & lighter sporules of cryptogamic plants, or the eggs ova of infusoria might be carried wafted. Considering that dust has fell on the Princess Louisa, when exactly half way between the country country north of the Senegal & the coast Cayenne; it is it not probable, that the living Infusorian found living at Cayenne & in the dust which fell north off the Cape Verd Isld, may have originally been transported from Africa to S. America?

I will conclude by remembering When we remember how many observers have described the hazy atmosphere dus & even discoloured sea far off the coast of Africa, & how often dust in considerable quantities

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(A)

The dust collected on the 8th in Lat 19°. 57' N. & Long: 24°: 5' W. is that, in which Prof. Ehrenberg found numerous finds, is almost composed of an Infusorian, iden identical with a species from Cayenne in S. America.

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has been blown during five months in the year, to great  distances over the Atlantic, I think we cannot can hardly doubt that here we see a powerful agency the wind is here here a powerful agent in the formation of a widely extended deposit; & this deposit, it appears from the observations of Prof. Ehrenberg, will consist in great part of Infusoria, unmingled free, I may add, over along a wide extent great space of arid coast, from the alluvial matter of any river.)

(N.B. Mr Fletcher Please to write these notes in their order of 1. 2. 3 &c)

List of References

*(3) (3) Edinburgh. New Phil Journal vol. 63 32. p. 134. An account from Berghaus' Almanack of the dust which fell during five days on the Princess Louisa

*(2) (2) Lieut James' observations were made on boar

Geographical Journal. Vol. VI IV p. 296. "Survey of some of the Canary Isd & part of coast of Africa by Lieut. W. Arlett. R.N."

*(4) (4) Lieut James' observations were made on board H.M.  Packet, Spey in 1838

*(5) (5) Nautical Magazine 1838. p. 824. A critic on the Paper above referred to in this Journal of the previous year, given are quotes from Roussin's survey in 1817, & gives other facts.

*(6) Horsburgh. E. Indian Directory p. 11

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Clark doubts dust between Canaries & C. Verde group, [though] near each — considers it yet volcanic

a distance of 300 miles, with the wind N.E. & the horizon hardly visible had the sails, rigging & masts covered with red dust. The nearest land was 600 miles distant. The same phænomenon was observed by Mr. Burnett in 1836.

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*(8) Proceedings of the Geolog. Soc 1839 v ol IV. p. 145. the Rev W. B. Clarke gives an account of dust which fell off the Cape Verd archipelago during three days: Lat 11° 3' N when 300 miles from land

In Turner's History of World p. 149. there is an account by Mr Forbes of dust which fell on a ship when 600 miles from the mainland. In the Edinburgh New Phil Journal. 1822 p. 402, there is another account by Mr Alexander of dust [text excised]