MARINE DEPOSITS 223 



dredged in the same regions as the sharks' 

 teeth, impregnated and coated with mangan- 

 ese in a similar manner. Such remains of 

 sharks and whales have evidently lain for 

 long periods of time exposed to the solvent 

 action of the sea- water, as many of them belong 

 to tertiary and extinct species (see Plate 

 XII.). 



Cosmic Spherules. — The materials derived 

 from extra-terrestrial regions, though inter- 

 esting on account of their origin, are of small 

 size and comparatively rare. They consist 

 of (1) black magnetic spherules frequently 

 with metallic nuclei, and (2) brown chondritic 

 spherules with crystalline structure, and are 

 supposed to have formed at one time part of 

 the tails of meteorites. They are usually 

 found in the deposits from very deep water, 

 especially from some of the red clay areas, 

 doubtless because few other materials there 

 reach the bottom to cover them up (see Plate 

 XII.). 



Zeolites. — Zeolites are represented in the 

 deposits of very deep water, especially in 

 the red clays of the Central Pacific, by phillip- 

 site, a silicate of calcium and aluminium, the 

 constituents of which are derived from the 

 decomposition of volcanic materials. It occurs 

 in crystalline form : as isolated elongated 

 crystals, twins, and aggregates of different 



