TRANSACTIONS OF SECTION B. 583 



6. On Manganese Nodules, and their Occurrence on the Sea-hottom. 

 By J. Y. Buchanan. 



The specimens exhibited consist of two nodules fi-om the South Pacific and of 

 ■several from Loch Fyne in Scotland, a number of manganiferous worm-tubes and 

 two samples of the mud in which these tubes and nodules are found in Loch Fyne. 

 I have besides some very curious specimens of cobalt nodules from New Caledonia, 

 which I owe to the kindness of my friend Professor Liversidge, of the University of 

 ■Sydney. These have come into my hands only within the last few days and I 

 exhibit them as curiosities which may have an interest for some of the members 

 present. 



My method of dredging for mud consists in anchoring the vessel by a dredge in 

 tlie form of a Trotman's anchor, which carries a frame instead of a bar connecting 

 the flukes. To this frame is lashed a bag which receives the mud which might 

 otherwise drop ofi" the anchor on heaving up. This method has proved successful 

 in two ways: first, by keeping the vessel stationary while the anchor is down, and 

 so admitting of temperatui'e-observations being made and water samples being 

 collected without having to resort to troublesome manoeuvres; and, secondly, by 

 bringing up a large specimen of the mud taken, not from the soft surface layer, as 

 is the case with the flat dredge, but from the underlying and stiffer material. 



My first and best haul of manganese nodules, however, was brought up on an 

 •ordinary kedge anchor and adhering to its flukes. A portion of this mud is exhi- 

 bited. It is from the deepest part of Loch Fyne, between Tarbert and Skate 

 Island. It was described in ' Nature ' of October 10, 1878. I have never succeeded 

 in getting mud so rich in nodules again. Part of it when sifted was found to 

 consist of 30 per cent, manganese nodides, 7"6 per cent, shells, and 62-5 per cent, of 

 sandy clay. I doubt very much if even the richest bottom in the Pacific contains 

 a like proportion. The other two samples of nodule-bearing mud are, as nearly 

 as possible, from the same locality ; but though they contain plenty of nodules, 

 these nodules are of a smaller average size, and are present in much smaller propor- 

 tion to the rest of the mud. Of the nodules collected on the first occasion, in 1878, 

 the average weight was 1'7 grammes ; of those collected last July the average 

 weight, after eliminating all that passed through a sieve of four meshes to the 

 inch, was only 0'42 grammes, and the proportion of nodules to mud would cer- 

 tainly not be more than 5 per cent. The whole of the mud which came up on 

 this occasion was sifted, with the exception of a small sample dried as it was ; 

 the nodules were then sorted by sieves of diflPerent degi-ees of fineness. The bulk 

 of them were retained by a ^-inch mesh. The nodules so retained weighed 307 

 ^•ammes, and numbered 726, and it is remarkable that besides these nodules there 

 was nothing on the sieve but a few fragments of shell and ttvo pebbles. This aflbrds 

 very strong evidence that the nodides are formed in situ, and cannot have been 

 washed into their present position, as in that case they woidd certainly have been 

 accompanied by pebbles. 



Hitherto the deep portion of Loch Fyne above alluded to is the only 

 locality in Scottish waters where I have found the oxide of manganese occiu*- 

 ring as nodules. It is, however, widely distributed, encrusting shells and as worm- 

 tubes, notably in the channel between Garvelloch Islands and the Island of Scarba 

 and in Loch Sunart, Similarly during the cruise of the Challenger, besides the 

 many locaUties where the nodules abounded, it was constantly found encrusting 

 shells in calcareous bottoms which were devoid of nodules. 



The Loch Fyne nodules i-esemble the oceanic ones in nearly every particular. 

 They are comparatively soft when first brought up, and become harder when 

 exposed to the air. Heated in the closed tube they give ofi" water charged with 

 ammonia and empyreimiatic products. When treated with hydrochloric acid the 

 soluble constituents are removed, and what remains behind includes the insoluble 

 constituents of the surrounding mud. Many of the Loch Fyne nodides have soft 

 kernels, which are richer in oxide of manganese than the rinds. 



A considerable number of determinations have been made, both of the available 

 oxygen and of the manganese ; and if the manganese found be united to the whole 



