154 



DEPTHS OF THE OCEAN 



Extra- 

 terrestrial 

 materials. 



land in those regions of the ocean affected by floating icebergs. 

 The dust from deserts, Hke volcanic dusts, may be carried by 

 wind to great distances from land, and can be detected in deep- 

 sea deposits, for instance, off the west coast of Africa. 



The materials of extra-terrestrial origin, though extremely 

 interesting, do 



not bulk largely ^'^^^^m ^ h 



in marine de- ^' ' 



posits ; indeed 

 they are rather 

 of the nature of 

 rarities, and are 

 noticed most 

 abundantly in 

 Red clay areas 

 where, for many 

 reasons, it is 

 believed the rate 

 of deposition is 



at a minimum. They consist of minute black metallic spherules 

 and brown chondritic spherules, which may be extracted by 

 the aid of a magnet when the Red clay deposit is reduced to 

 a fluid condition by admixture of water. The black spherules 

 (see Figs. 130 and 131) sometimes have a shining metallic 



V 



Canna/'/a lamarckii. Per 



of this species are occasionally met with 



Fig. 122. 

 and Les. (From Steuer. ) 



The fragile shells 

 deep-sea deposits. 



Fig. 123. 



Pterotrachea coi'onafa, Forsk. (From Leuckart, after Steuer. ) This species has no shell, 

 and therefore does not enter into the composition of deep-sea deposits. 



nucleus of native iron (or an alloy of iron, cobalt, and nickel), 

 surrounded by a shell of brilliant magnetic oxide of iron, to 

 which the magnetic properties of the spherules are due. The 

 brown spherules (see Figs. 132 and 133) have the lustre of 

 bronze externally, and have a finely lamellatefd crystalline 

 structure, with blackish -brown inclusions of magnetic iron, 

 which account for their extraction by the magnet. A cosmic 



