FALLS OF DUST IN THE ATLANTIC. 623 



So thick was it, that a young man having fallen overboard, the boats which 

 were lowered in search of him could neither find him, nor scarcely find 

 the ship for some time afterwards, and this though guns were fired." 



From the several recorded accounts,* it appears that the quantity of 

 Dust which falls on vessels in the open Atlantic is considerable, and that 

 the atmosphere is often rendered quite hazy ; but nearer to the African 

 ■coast the quantity is still more considerable. Vessels have several times 

 run on shore, owing to the haziness of the air ; and Horsburghf recom- 

 mended all vessels, for this reason, to avoid the passage between the Cape 

 Verde Archipelago and the mainland. Eoussin, also, during his survey, 

 was thus much impeded. Lieut. Arlett found the water so discoloured,^ 

 that the track left by his ship was visible for a long time ; and he attri- 

 buted this, in part, to the fine sand blown from the deserts, " with which 

 everything on board soon becomes perfectly caked. "§ 



Professor Ehrenberg has examined the Dust collected by Lieut. James 

 and myself ; and he finds that it is in considerable part composed of Infu- 

 soria, including no less than sixty-seven different forms. These consist of 

 thirty-two species of siliceous-shielded Polygastrica ; of thirty-four forms 

 of Phytolitharia, or the siliceous tissues of plants ; and of one Polythalamia. 

 The little packet of Dust collected by myself would not have filled a quarter 

 of a teaspoon, yet it contains seventeen forms. Professor Ehrenberg re- 

 marks that, as thirty-seven species are common to several of the packets, 

 the Dust collected by myself, and on four successive days by Lieut. James, 

 must certainly have come from the same quarter ; yet mine was brought 

 by an E.N.E. wind, and Lieut. James' by a S.E. and E.S.E. wind. The 

 Infusoria are all old known species, excepting one allied to a Hungarian 

 fossil ; and they are of fresh-water origin, with the exception of Gramma- 

 tophora oceanica and Textilarea globulosa, which are certainly marine. 

 Professor Ehrenberg could not detect any of the soft parts of the Infusoria, 

 as if they had been quickly dried up, and hence it would appear that they 

 must have been caught up by the wind some time after their death. 



The greater number of the species are of wide distribution ; four species 

 are common to Senegambia and South America, and two are peculiar to 

 the latter country; moreover, it is a very singular fact, that out of the many 

 forms known to Professor Ehrenberg as characteristic of Africa, and more 

 especially of the Sahara and Senegambia regions, none were found in the 

 Dust. From these facts, one might at first doubt whether the Dust came 

 from Africa ; but considering that it has invariably fallen with the wind 

 between N.E. and S.E., that is, directly from the coast of Africa; that the 

 first commencement of the haze has been seen to come on with these winds ; 

 that coarser particles have first fallen ; that the Dust and hazy atmosphere 

 are more common near the African coast than farther in the Atlantic ; and, 



• Nautical Magazine, 1837, page 291 ; Edinburgh Philosophical Journal, vol. vii., 

 page 402 ; Howard Malcolm's Travels, vol. ii., page 200, 

 t Horsburgh's East India Directory, page 11. 

 J In Tuckey's Nanrative of the Congo Expedition, pi^e 10. 

 ^ Nautical Magazine, 18i7, page 354. 



