in the Ocean at the South Pole. 179 



sphere off the Cape Verd Islands, and also on the high sea of 

 that region, while he was there ; and likewise on a ship, which, 

 according to the account in his letter, was 380 sea-miles distant 

 from land. The wind was then blowing from the African coast. 

 Mr. Darwin has sent to the author for examination a sample of 

 the dust which fell on the ship on the high sea at that great 

 distance from land. This dust has been universally regarded 

 hitherto as volcanic ashes. The microscopic analysis has clearly 

 shown that a considerable portion, perhaps one-sixth of the mass, 

 consists of numerous species of Siliceous Polygastrica and por- 

 tions of silicated terrestrial plants, as follows : — 



A. SILICEOUS POLYGASTRICA. 



1. Campy lodiscus Clypeus. 10. Himantidium Arcus. 



2. Eunotia Amphioxys. 11. — Papilio. 



3. — gibberula. 12. Navicula affinis ? 



4. GallioneUa crenata. 13. — lineolata. 



5. — distans. 14. — Semen. 



6. — granulata. 15. Pinnularia borealis. 



7. — marchica. 16. — gibba. 



8. — procera. 17. Surirella (peruviana ?) . 



9. Gomphonema rotundatum ? 18. Synedra Ulna. 



B. SILICEOUS PHYTOLITHARIA. 



19. Amphidiscus Clavus. 29. Lithostylidium Ossiculum. 



20. Lithodontium Bursa. 30. — quadratum. 



21. — curvatum. 31. — rude. 



22. — furcatum. 32. — Serra. 



23. — nasutum. 33. — spiriferum. 



24. — truncatum. 34. Spongolithis acicularis. 



25. Lithostylidium Amphiodon. 35. — aspera. 



26. — clavatum. 36. — mesogongyla. 



27. — cornutum. 37. — obtusa. 



28. — - lseve. 



The forms included in this catalogue, mostly known and for 

 the most part European, prove — 



it That this meteoric shower of dust was of terrestrial origin. 



2. That it was not volcanic ash. 



3. That it was dust which had been lifted up to a great height 

 from a dried-up marshy district by an unusually strong current 

 of air or a whirlwind. 



4. That the dust did not necessarily and evidently come from 

 Africa, as being the nearest land, although the wind blew from 

 thence when the dust fell ; for this reason, that no exclusively 

 African forms are among it. 



5. That as Himantidium Papilio, a very marked form, has hi- 

 therto occurred only in Cayenne (see the Mikroskopische Leben 

 in SUd- und Nord-Amerika, plate 2. fig. 2.), and as the Surirella 

 is also probably an American form, only two conclusions present 

 themselves ; either that the dust was raised in South America into 



