7:'»<') DK JOHN MURRAY AND MR ROBERT IRVINE ON THE 



of manganese dioxide disseminated throughout the deposit. When dredgings have been 

 obtained in these Globigerina deposits, many manganese nodules have been procured, 

 but they were not accompanied by large numbers of sharks' teeth, bones of cetaceans, 

 zeolitic crystals, and cosmic spherules, as in the case of the Red Clays. Very rmnry 

 minute particles of basic volcanic rocks, most of them in an altered condition, were, how- 

 ever, present in these dark chocolate coloured Globigerina Oozes. 



'Hie one outstanding fact connected with the distribution of manganese nodules in 

 the abysmal regions of the ocean is, that wherever they occur in great abundance, they 

 are accompanied by numerous fragments and lapilli of basic volcanic rocks, and many 

 of these, on examination, are found to be in an advanced state of alteration. For instance, 

 a typical Globigerina Ooze is usually of a white or rose colour, and the inorganic residue, 

 insoluble in dilute acids, consists of clayey matter, oxides of iron, and a few mineral 

 particles chiefly of volcanic origin, along with fragments of pumice. In such a typical 

 deposit, a few grains of manganese dioxide may be observed attached to some of the 



Foraminiferal shells, or in the residue after removal of the 

 carbonate of lime by dilute acid. As a rule, no manganese 

 nodules are procured by dredging on such a typical Globi- 

 gerina Ooze. A Globigerina deposit with the same species 

 of Foraminifera, the same percentage of carbonate of lime, 

 laid down in similar latitudes and under similar physical 

 conditions, but containing much volcanic debris of a basic 

 character, is, however, of a dark chocolate colour, and con- 

 tains many manganese nodules. 

 ' 'LVw Se5y b rbeddedt°dt Indeed, all observations go to show that the quantity of 



positions of manganese (natural manganese dioxide in these abysmal deposits is in direct 



size). Station 160 ; 2600 fathoms. . . x 



Southern Indian Ocean. relation to the abundance and basic character of the erupted 



rocks and minerals associated with them, and the extent to which these minerals and 

 rock particles have undergone alteration. 



In the Blue Muds, which in deep water surround continental land and cover the 

 bottoms of enclosed or partially enclosed seas, no manganese nodules similar to those from 

 the central regions of the ocean basins have as yet been obtained in dredgings. In a 

 good many instances, however, stones and boulders have been dredged from Blue Muds or 

 other terrigenous deposits, with the upper or emerged surfaces coated with manganese. 

 Markings of this substance were also found on some shells, fragments of pumice, and 

 phosphatic concretions which evidently had lain on the immediate surface of the mud. 

 The Blue Muds in deep water have a thin red-coloured watery layer on the surface, and 

 beneath this the deposit is of a dark blue colour, and often smells strongly of sulphur- 

 etted hydrogen. These deeper layers contain much decomposing organic matter, like 

 i he muds of the Clyde Sea-Area, and in them no deposits of manganese have as yet 

 been found other than mere traces; but manganese dioxide was found coating objects 

 lying on the immediate surface layer, and, as in the case of the Clyde mud, these 



