January 10th, 1832. Four days out from Tenerife at 10° 10°12’ west longitude and 40° north latitude when the temperature was 51.5°, the ship was subjected to a remarkable meteorological phenomenon. During the morning, in the space of some ten minutes, the entire deck of the Beagle was deluged with dust and the surface of the sea also, seemingly for a distance of about two hundred yards about our vessel in all directions. Though the dust descended from the sky, the sun was still visible through the pall of dust and, beyond the darkness created by the dust, there were no clouds visible. The descent of the dust was not even and I took pains to observe its passage in its eddies and in the singular patterns it made upon the deck. It is hardly possible to convey the sense of elevated wonder that I experienced as I watched the descent of these particles. However it was rapidly noticed by all that the debris on the deck gave off a sulphurous smell that was anything but heavenly and which added considerably to the distress of those detailed to swab the deck. Indeed until their labours were concluded the whole ship bore a most wretched and unsailorlike aspect and I noticed that the elevation of my spirits gave way to a sense of oppression. The affair was most remarkable and I could not have credited it had I not had ocular demonstration of the same. However I discovered on making enquiry from some of the crew at work on the deck that such visitations are by no means unfamiliar during ocean crossings and the interested reader may find other instances cited in Captain FitzRoy’s account of the matter as it was presented to the Admiralty.

The opinion earlier expressed by Chamisso in his Tagebuch that such rains of dust may have been collected, conveyed and deposited by whirlwinds should now be discounted for I observed no turbulence in the ship’s rigging that could correspond to the proximity of a whirlwind. With the help of Mr (now Captain) Sullivan, I was able to collect a considerable quantity of this dust, weighing a little over four pounds and, when I returned to England some four years later, I was able to have the dust which had been preserved in flasks subjected to analysis under the microscope. The contents of the flasks were shown to be compounded of a considerable variety of materials. Most striking was the presence of a type of fine silicate grit so far thought to be peculiar to the Great Asian Desert of the Gobi. There was also a considerable amount of organic matter such as fragments of the bodies of cockroaches and other insects of the Blattidae class as well as cobwebs, fungal spores and even particles of dried blood – whether human or animal it was not possible to determine. By far the largest constituent in these flasks was however common dust such as may be found on the floor of any London household. Captain FitzRoy’s suggestion that the dust fall was of volcanic origin, though intelligent, is proved by this analysis to be wide of the mark. The circumstance of common household dust being deposited so far out in the Atlantic is mysterious. Nevertheless it is plainly a manifestation of the material world and partakes of nothing of the supernatural. Here I leave the topic, for we were not subjected to any further manifestations of a similar kind and I was glad to find my interest taking me in other directions.

The Voyage of the ‘Beagle’, by Charles Darwin (1845)