IV DEPTHS AND DEPOSITS OF THE OCEAN 153 



or basic, and andesitic. After pumice, the most striking volcanic 

 products are fragments of basic volcanic glass (sideromelan) 

 nearly always partly, sometimes entirely, decomposed and 

 altered into palagonite, together with palagonitic tufas, generally 

 associated with the deposition of the peroxides of manganese 

 and iron, besides basaltic and other lapilli and volcanic ashes. 

 Great slabs have been dredged showing sometimes distinct 



Fig. 121. 



pelagica, d'Orbigny. 



From the surface {^x)- 



layers produced by showers of volcanic ashes. Minerals of 

 volcanic origin (volcanic dusts) may be carried great distances 

 by the winds, and ultimately find a resting-place on the bottom 

 of the sea. 



The continental products consist of fragments of continental Continental 

 rocks and the minerals derived from their disintegration, the Products. 

 characteristic mineral species being quartz. The rock-fragments 

 are usually found only in close proximity to the continental 

 land-masses, though exceptionally found in deep water far from 



