1042 
THE VOYAGE OF H.M.S. CHALLENGER. 
From the preceding analyses it appears that deep-sea bones, like fossil ones, contain a 
far larger proportion of fluorine than recent bones. This fluorine cannot be assumed 
to be the original fluorine of the bones, but must be supposed to owe its origin to a 
continuous, though slowly progressing, double decomposition between the phosphate of 
the bone and the trace of dissolved fluoride in the sea water. 
To test this view I have made the following experiment : — 10 grms. of precipitated 
tricalcic phosphate (undried) were digested for six weeks in a solution of 30 grms. of 
common salt and 2 grms. of fluoride of sodium, in 1 litre of water ; the precipitate was 
then collected on a filter, washed free from chlorides (and dissolved fluorides), dried, 
ignited, and tested quantitatively for fluorine by means of the method used for the 
bones. 5 grms. of ignited substance gave 0T20 grms. of fluorine = 2‘41 per cent., equi- 
valent to 4*95 per cent, of fluoride of calcium. It is quite reasonable to admit that what 
the 0'2 per cent, of fluoride of sodium in the solution employed effected in six weeks, the 
trace of fluoride in actual sea water (small as it is) may accomplish in thousands of years. 1 
The “ manganese oxide ” which was found diffused through, or at least as a deposit 
on, the surface of all the deep-sea bones examined, no doubt owes its origin to a slow 
decomposition of extraneous mineral matter in which the bones at some stage of their 
existence got embedded . 2 
MANGANESE NODULES. 
These concentrations of ferric and manganic oxides, mixed with argillaceous materials, 
whose form and dimensions are extremely variable, belong generally to the earthy 
variety or wad, but pass sometimes, though rarely, into varieties of hydrated oxide of 
manganese with distinct indications of radially fibrous crystallisation. The interpretation 
adopted, in order to explain the formation of these manganese nodules, is the same as that 
which is admitted in explanation of the formation of coatings of this material on the 
surface of terrestrial rocks. These salts of manganese and iron, dissolved in water by 
carbonic acid, then precipitated in the form of carbonate of the protoxides of iron and 
manganese, become oxidised, and give rise in the calm and deep oceanic regions to more 
or less pure ferro-manganiferous concretions. The following analyses are of nodules from 
two Stations, one in the North and the other in the South Pacific. — John Murray. 
1 It may be that, owing to the fluoride of calcium being less soluble than the phosphate, a relatively large quantity 
of the former remains in the bones as the latter is dissolved away. In comparing the analyses of the bones and teeth 
dredged from the bottom of the sea with those of recent animals, the elimination of gelatinous organic matter from 
the former is very striking. These facts added to others support the view of the great antiquity of the deep-sea 
specimens. — J. M. 
2 On the Distribution of Volcanic Debris over the Floor of the Ocean, &c., by John, Murray, Proc. Roy. Soc. Edin., 
vol ix. p. 256, 1877. 
