THE WORLD'S LUMBER ROOM. 



lected only on a damp sponge ; but it has been known to 

 fall on vessels one thousand and even sixteen hundred miles 

 from any land. 



From the direction of the wind, and the fact that the 

 dust falls during those months when the harmattan raises 

 clouds of it high in the air, and blows from the north- 

 west shores of Africa, it 

 was at first naturally con- 

 cluded that the dust was 

 all African too. The 

 mineral part of it, no 

 doubt, may be so ; but 

 on examination it was 

 found that the greater 

 part of the dust was or- 

 ganic, and consisted 

 mainly of those minute, 

 Fig. 5 . DIATOMS. flint-cased forms of plant- 



life known as diatoms, 



which exist in almost all water salt, fresh, or brackish 

 (Fig. 5). Further examination also revealed the singular 

 fact that, though the dust came directly from Africa, of 

 all the many different organic forms none were peculiar to 

 Africa, and all but two belonged to fresh-water families ; and 

 it has since been proved that all the organic portion of the 

 dust, whether it fall at Cape Verd, Malta, Genoa. Lyons, or 

 in the Tyrol, has come from the south side of the equator, 

 and has been transported from the banks of the Orinoco and 

 Amazons. 



When, however, we find that particles of mineral matter 



