i6o 



DEPTHS OF THE OCEAN 



silicate phillipsite occurs in the pelagic deposits, and is supposed 

 to be a secondary product derived from the decomposition of 

 volcanic rock fragments. Phillipsite is found in the various 

 kinds of deposits in the deep water of the Central Pacific and 

 Central Indian Ocean far from land, and is most abundant in 

 some Red clay areas. It occurs in crystalline form, either as 

 simple isolated microliths, crossed twins, irregular groups, or 

 aggregated into spherolithic groups in which these zeolitic 

 crystals are entangled together so as to form crystalline globules 

 of sufficient size to be distinguished by the naked eye. The 

 distribution of these crystals of phillipsite coincides with that of 

 basic volcanic glasses and basaltic lapilli over the ocean-floor, 

 the decomposition of which, under 

 the action of sea-water, would give 

 rise to the materials afterwards 

 deposited in a free state as zeolitic 

 crystals and aggregates. 



Radio-active Professor Joly has examined 



substances. ^^^ their radium contents a number 

 of deposit-samples supplied by Sir 

 John Murray. He finds that the 

 deep-sea deposits are much richer 

 in radium than the average terres- 

 trial rocks. The Red clays and 

 the Radiolarian oozes, which are 

 laid down in deep water far from 

 land, contain much more radium 

 than the calcareous deposits like the Pteropod and Globigerina 

 oozes. The radio-activity and percentage of calcium carbonate 

 in the deposits stand in an inverse ratio to each other, and the 

 ■ Blue muds contain less than the calcareous oozes, though more 

 than the continental rocks. It seems evident that the quantity 

 of radio-active substances, of manganese nodules, with earbones 

 of whales and sharks' teeth, of zeolitic crystals and cosmic 

 spherules, is greatest where, for other reasons, we believe the 

 rate of deposition to be least. 



Deep-sea In the neighbourhood of emerged land the material derived 



deposit types, f^^^^ |.j^^j- \^^^ jg spread over the sea-floor, becoming finer and 



finer in texture with greater distance and depth, whereas in 



the central regions of the great ocean basins land-detritus may 



be almost totally absent from the deposits, while the calcareous 



Fig. 135. — Manganese Nodule with 

 TWO Tunicates and a Brachiopod 

 attached. 

 "Challenger" Station 160, Southern 

 Ocean, 2600 fathoms. 



