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Proceedings of the Roycd Society 
olivine, augite, or hornblende, and these apparently undergoing 
decomposition and alteration, or where we have evidence of great 
showers of volcanic ash, there we find the manganese in greatest 
abundance. This correspondence between the distribution of the 
manganese and volcanic debris appears to me very significant of 
the origin of the former. I regard the manganese, as we find it, 
as one of the secondary products arising from the decomposition of 
volcanic minerals. 
Manganese is as frequent as iron in lavas, being usually asso- 
ciated with it, though in very much smaller amount. In magnetite 
and in some varieties of augite and hornblende the protoxide of 
iron is at times partially replaced by that of manganese. 
In the manganese of these minerals, and in the carbonic acid 
and oxygen of ocean waters, we have the requisite conditions for 
the decomposition of the minerals, the solution of the manganese, 
and its subsequent deposition as a peroxide. 
The carbonic acid converts the silicates of the protoxides of 
manganese, and the protoxides of manganese into carbonate of 
manganese, and thus prepares the way for oxidation by the oxygen 
of the water. 
It is probable that the action of the carbonic acid is not apparent, 
and that the manganese is at once deposited as a high oxide if not 
as the peroxide. This theory is essentially the same as that which 
Bischof gives for manganese ores generally. I have laid a series of 
these manganese depositions on the table. An inspection of these 
and their localities will show that in the clays and oozes the depo- 
sitions are nodular in form. If a section be made of one of these, 
a number of concentric layers will be observed arranged around a 
central nucleus — the same as in a urinary calculus. When the 
peroxide of manganese is removed by strong hydrochloric acid, 
there remains a clayey skeleton which still more strongly resembles 
a urinary calculus. 
This skeleton contains crystals of olivine, quartz, augite, magne- 
tite or any other materials which were contained in the clay from 
which the nodule was taken. In the process of its deposition 
around a nucleus, the peroxide of manganese has inclosed and 
incorporated in the nodule the clay and crystals and other materials 
in which the nucleus was imbedded. The clayey skeleton thus 
