Annotated record of the detailed examination of Mn deposits from the H.M.S. Penguin expedition to the Coral Sea

The analyses of the samples from the Balfour Shoal show that these deposits contain a very large quantity of carbonate of lime, ranging from 88.7 per cent, on the summit to 71.9 per cent, in the deeper water at the base of the cone. The decrease in the quantity of carbonate of lime with increase of depth is not quite regular; still, a general fall in the percentage of lime is clearly indicated from shallower to deeper water. As might be expected in such a circumscribed area, there is a great uniformity both in the chemical composition and relative abundance of the organic and inorganic constituents of the deposits. In all cases the carbonate of lime is almost wholly made up of the dead shells which have fallen from the surface waters - belonging to Plankton organisms such as Pteropods, Heteropods, pelagic Foraminifera and coccoliths. The calcareous shells were in very many cases discoloured brown or black by depositions of the peroxide of manganese. On the north-east steep side of the Balfour Shoal there were indications that depositions of manganese peroxide were more abundant than elsewhere. In 1645 fathoms, there was an angular fragment of a mottled yellowish jasper coated with manganese peroxide, and in 1570 fathoms there were three characteristic spherical black manganese nodules from one-half to three-fourths of an inch in diameter, quite similar to those procured by the Challenger in many areas of the Pacific and Atlantic. In one of these nodules the nucleus was a sub-angular fragment of a light-coloured augite-granophyre.