MANGANESE OXIDES AND MANGA.NESE NODULES IN MARINE DEPOSITS. 741 



evidence that these spherules have an extra-terrestrial origin.* But these cosmic 

 spherules make up a very small part of the whole deposit. While admitting that a very 

 small quantity of the iron and a still smaller quantity of the manganese in abysmal 

 deposits have originated in the fall of meteorites to the earth, still it is undoubted that 

 the great bulk of the manganese and iron in the manganese nodules has been derived 

 from terrestrial rocks. 



Dieulafait,! from an examination of some samples of sea-water from the Atlantic 

 and Indian Oceans, came to the conclusion that manganese existed in sea-water in 

 the form of soluble bicarbonate, which becoming oxidised at the surface of the sea 

 then fell to the bottom as oxides, and there took on a concretionary form. We have 

 shown that, while manganese carbonate exists in the water associated with the clays, 

 muds, and oozes at the bottom of the ocean, yet, so far as our researches go, there are no 

 traces of manganese in solution in the great body of oceanic water. Traces of manganese, 

 however, may be found in suspension in almost any sample of ocean water, associated 

 with the suspended clayey matter which is nearly always present. This view of 

 Dieulafait, as well as that of Eenard,| that the greater part of the manganese 

 accumulated at the bottom of the ocean has been derived from manganese in solution in 

 the waters of the ocean, must therefore be abandoned. Besides, the distribution of the 

 manganese dioxide in marine deposits in no way corresponds to what would take place did 

 it fall to the bottom everywhere on oxidation of its carbonate at the surface of the ocean, 

 even taking into consideration the rate of accumulation of the different kinds of deposits. 



Mr J. Y. Buchanan, the chemist of the Challenger Expedition, has referred the 

 origin of manganese nodules to the intervention of living organisms, it being held 

 that the fine mud which some deep-sea organisms pass through their alimentary 

 canals undergoes chemical changes, sulphuretted hydrogen and sulphides of iron and 

 manganese being formed, the latter becoming subsequently oxidised. Those animals, such 

 as Annelids, Holothurians and other Echinoderms, which obtain their food in this way, 

 feed only on the thin red-coloured surface-layer of a Blue Mud. The excreta found in 

 this layer are all red-coloured, so that if sulphide of iron be formed within the bodies of 

 the animals, it must again be reoxidised after evacuation. The blue colour of the excreta 

 found in the deeper layers is no doubt due to sulphide of iron, but this blue colour is 

 an effect of the accumulation of the deposit as a whole, and arises from the decomposition 

 of the organic matters imprisoned in the deeper layers by the gradual accumulation at 

 the surface of the deposit. It has been shown that sulphide of manganese cannot exist 

 under the same conditions as the sulphide of iron, but immediately passes into carbonate 

 of manganese, which again passes to dioxide in the presence of the oxygen of the super- 

 incumbent sea-water. These changes take place not directly through the action of living 

 organisms, but through the decomposition of organic debris present in the muds. Did the 

 formation of manganese nodules in any way depend directly on the activity of living 



* Murray and Renard, Deep-Sea Deposits Chall. Exp., pp. 327-336. 



t Dieulafait, Comptes rendus, torn. xcvi. p. 718, 1883. 



1 Murray and Renard, Deep-Sea Deposits Chall. Exp., p. 372, note. 



VOL. XXXVII. PART IV. (NO. 32). 5 U 



