MANGANIFEROUS NODULES IN BOULDER-CLAY. 139
with a large quantity of sand." It is possible that the two
materials have a similar source; both are found only in soils
overlying clay and which contain chalk. Probably an abun-
dance of chalk is necessary for the formation of the nodules, as
it is well known that whereas in the presence of acids manganese
exists in its stable compounds in the manganous state, in the
presence of alkali it becomes oxidised and forms the manganic
compounds. Therefore in an alkali or chalky soil alone could
nodules or cement, in which manganese exists as the peroxide, be
formed. Manganese peroxide is usually found, as in these cases,
associated with ferric oxide and the lower oxide of manganese.
The following may be the explanation of the occurrence of
these nodules:—Surface soil contains the silicates of iron and
manganese, but these are decomposed by the soil acids, and
salts of iron and manganese are formed in solution. In the presence
of an alkali these salts decompose and precipitate the oxides
of the metals. At the same time the manganese being in the
condition of a free oxide would become more fully oxidised by
the action of the air in the soil. To prove the truth of this
supposition a solution of manganese sulphate was taken and on
the addition of ammonia or other alkali, oxidation at once took
place in the presence of air, the white precipitate first formed
becoming brown, and in the course of 24 hours almost black.
This precipitate on examination was found to consist partially of
the higher oxide of manganese liberating chlorine from hydro-
chloric acid. The slightest acidity, even that caused by excess
of carbonic acid in the solution, was sufficient to prevent this
oxidation even when so powerful an oxidiser as hydrogen per-
oxide was employed. This precipitation may resemble crystal-
lization, in taking place from a particular point, and the sand
adhering to the growing particle would become cemented up into
the nodule.
[At the reading of the paper, Mr. T. S. Dymond, F.I.C,
F.C.S., made some remarks, which are printed as follows in the
form of a Note :—
Manganiferous nodules are not infrequently met with on the bed of the
deep sea. They have been found near the Canaries, to the south west of
Australia, in the Northern Pacific Ocean and elsewhere. These nodules are
said to have the appearance of urinary calculi, are brown in colour and have
a structure shewing superposed layers of clay. Analysis shews that they
consist chiefly of the oxides of iron and manganese, the latter peroxidized,