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XVII. — On the Composition of Oceanic and Littoral Manganese Nodules. 

 By J. Y. Buchanan, Esq., F.RS. (With Map and Plate.) 



(Read January 9, 1891.) 



The following analyses were made some years ago, principally with the object of 

 ascertaining the state of oxidation of the manganese in the nodules. The nodules 

 examined came from three different localities, two of them oceanic and the third littoral. 

 Samples marked I., II., and III. are from nodules brought up in the trawl on board the 

 "Challenger," on 13th March 1874, in lat. 42° 42' S., long. 134° 10' E. The depth of 

 the water was 2600 fathoms, and the temperature of the bottom water 0'2 o C. The 

 density of the bottom water was 1*02570 at 15'56° C. Being from a high southern 

 latitude, and therefore near the source of surface aeration, the water is highly charged 

 with atmospheric gases, especially oxygen. It contained, per litre, 18 "4 c.c. of mixed 

 nitrogen and oxygen, of which 3T81 per cent, was oxygen, and 27'33 c.c, or 53"7 

 milligrammes, loosely-bound carbonic acid. The position of the station is about 400 

 miles south-west of the nearest part of the Australian coast, and about 500 miles west of 

 Tasmania. It was the deepest water observed in the Antarctic voyage between the Cape 

 of Good Hope and Melbourne. The Laul was a very abundant one, and a few notes 

 which I made at the time may be interesting : — " The water was found unexpectedly 

 deep, the bottom being red clay, with some Foraminifera. The bag of the trawl came 

 up quite full of this mud, with many animals and a large number of manganese nodules. 

 These were of all shapes, and with the characteristic mammillated surface, which in some 

 was accentuated to such a degree as to give them a botryoidal appearance, like specimens 

 of Psilomelane. Many of them were perfectly spherical, others formed groups of spheres. 

 One of these spherical nodules was found, on being broken, to contain a hard kernel of a 

 mineral, giving a powder of the colour of bichromate of potash, with a conchoidal fracture 

 and resinous lustre. Round this the spherical shells of manganese were gathered, and 

 could be easily broken off with the fingers. Another nodule was noticed with the same 

 yellow resinous-looking substance in the centre, but it mixed with the manganese forming 

 part of the substance, and could not be detached from the surrounding shells. It has a 

 light wine-yellow colour by transmitted light, and polarises light. Many flat pieces were 

 observed, with horizontal stratification and botryoidal surface. Whether flat or spherical, 

 the manganese was put on in layers, separated by very fine sheets of the mud of the 

 locality. There was one nodule which had formed round the fragment of another, and 

 therefore older nodule, the distinction between the two being well marked by the 

 inclination of the mud sheets of the kernel to those of the shell. There were many where 



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