372 
THE VOYAGE OF H.M.S. CHALLENGER. 
Oricfin of the Manganese and Manganese Nodules. — The source of the manganese, 
ami the mode of formation of the ferro-manganic concretions in marine deposits, have 
been the subjects of numerous publications. 
In 1877 Murray^ referred to the association of manganese with abundance of 
basic volcanic debris at the bottom of the ocean, and attributed the origin of the man- 
ganese nodules to the oxidation of the carbonate of manganese arising from the decom- 
position of manganiferous rocks, and its subsequent deposition in concretionary form. 
In 1878 Giimbel^ analysed some nodules sent to him by Willemoes-Suhm, a dis- 
tinguished naturalist of the Challenger Expedition, who died at sea. He recalls that 
Forchhammer had made known the presence of manganese in sea- water, and that Bischof 
had shown the presence of the same substance in the ashes of Zostera maritima. But 
he does not admit the concentration of manganese under the influence of organisms, 
because it is dissolved in sea-water in such small quantity, and because the manganese is 
found in great abundance over a large area of the sea-bed. He refers the formation of 
the nodules to the influence of submarine springs holding manganese in solution, which 
is precipitated on contact with the sea-water. Agglomerates of a rounded form are thus 
j)roduced by repeated turnings and rollings in the clay and water. 
In 1881 Buchanan suggested that the manganese nodules originated through the inter- 
vention of organic substances, which changed to sulphides the sulphates of the sea-water, 
thus causing the formation of sulphides of iron and manganese, these becoming subse- 
quently oxidised. Recently in 1890 he repeated this view.® 
In 1882 Boussingault ^ discussed the formation of coatings of manganese in various 
regions, due to the presence of water charged with compounds of this element. He rejects 
the views of Buchanan and Giimbel as insufficient to explain the facts, and holds that the 
submarine concretions and manganiferous coatings are derived from the carbonates. 
In 1883 Dieulafait® rested an explanation on the fact that sea-water collected between 
New York and ]\Iarseilles, as well as in the Red Sea and Indian Ocean, deposited in the 
* Proc. Roy. Soc. Edin., vol. ix. pp. 255-258, 1877 ; also Proc. Roy. Soc., vol. xxiv. p. 529, 1876. 
* Gunil>el, “Die am Grunde dea Meeres vorkommenden Manganknollen,” Sitzb. d. k. bayer. Akad. d. Wi$s., Math.- 
pliys. Cl., 1878, ii. pp. 189-209 ; also Neues Jahrb. f. Min., &c., 1878, p. 869. See also: le mineralogisclie-geologisclie 
IleschafTenlieit der auf der Forscliungsreise S.M.S. ‘Gazelle’ gesammelten Meeresgrund-Ablagerungen,” pp. 33-36, 
Berlin (no date). 
* Brit. Ass. R'TTort for 1881, pp. 58.3-4 ; Proc. Roy. Soc. Edin., vol. xviii. pp. 17-39. With reference to this view it 
may l>e stated that in our experiments at the Scottish Marine Station it was found that manganese dioxide, when 
exjsised to the action of Bul])huretted hydrogen or alkaline or earthy sulphides, becomes reduced to a lower oxide ; 
this reaction takes place when the manganese no<lules themselves are so exposed. For example, powdered manganese 
nodules were intrcxluced into sea-water, along with decomposing mussel-llesh ; in a few days the sulphates present in the 
sea-water had l»een reduced to sulphides, which firstly altered the manganese peroxide to protoxide, which, being soluble 
in the carl»onic acid (the j>ro<luct of the oxidation of the organic matter), remained as soluble bicarbonate of manganese 
in the sea-water, while the iron sesquioxide present in the nodules was thrown down as insoluble suli>hide. It does 
not therefore seem pfissible that the ikkIuIcs can be formed in the way indicated by Buchanan (Murray and Irvine). 
* “ Sur l'ap|sirition «lu manganiise a la surface des roclies,” Annales de Chimic et de Physique, 5th ser. tom. xxvii. ]']>. 
280-311, 1882. 
* “ Ijf manganl-sc dans les eatix de mcr actuclles et dans certains de leurs ddjxjts ; conscfjuences relatives a la craie 
blanche de la jM'riode iccondaire," C'omjdcs Rciutus, tom. xevi. p 718, 1883. 
