56 
Proceedings of Iioyal Society of Edinburgh. 
of sulphides of iron and manganese, which, on subsequent exposure 
to sea-water containing oxygen, are quickly oxidised — the manganese 
taking priority. 
It is obvious that any conclusion as to the relative correctness of 
these two theories cannot be arrived at solely by chemical con- 
siderations, but must depend largely upon such questions as the 
relative abundance and distribution of animal life upon the sea- 
floor ; and, further, upon the physical structure of the deposits. 
In this paper we propose to confine ourselves chiefly to the 
chemical aspect of the subject, and more particularly to certain 
reactions of manganese, which we believe to have a very direct 
bearing upon it. 
A. — Behaviour of Hydrated Protoxide of Manganese. 
If freshly-precipitated hydrated protoxide of manganese be added 
to sea-water, it is pretty freely dissolved, and if the sea-water be in 
large excess, the manganese remains in solutions for a very con- 
siderable time. If, however, more hydrated protoxide of manganese 
be added than is sufficient to form carbonate of manganese with the 
carbonic acid in the sea-water, the excess of manganese is pre- 
cipitated, after a comparatively short period, as hydrated oxide of 
manganese (more or less completely peroxidised), provided the 
water is sufficiently aerated. 
B. — Behaviour of Carbonate of Manganese. 
Carbonate of manganese, when freshly precipitated and amor- 
phous, dissolves in sea-water in notable quantity, but is very 
sparingly soluble in the crystalline form. Purther, when carbonate 
of manganese is dissolved in sea-water, it remains in solution. Such 
solutions do not give rise to any rapid production of peroxide of 
manganese. This is in accordance with what has been hitherto 
ascertained concerning the behaviour of carbonate of manganese, 
which, as has been shown by Bischoff and others, is very slowly 
oxidised under ordinary circumstances. A. Gorgeu ( Comptes 
Rendus, cviii. 1006-1009) states “that native manganese car- 
bonate or diallogite is very stable, and remains unaltered after 
contact with aerated water for three years. Precipitated manganese 
