1890 - 91 .] Mr J. Y. Buchanan on Sulphur in Marine Muds. 37 
Fe 2 (S0 4 ) 3 . Still there is always local formation of FeS which dis- 
appears on mixing, so that the reaction is really that of the whole 
cycle. The action, therefore, of MnS on soluble iron salts is in the 
first instance to reduce whatever is in the ferric state to the ferrous, 
and then at once to precipitate the ferrous salt as sulphide, a man- 
ganous salt taking the place of the ferrous salt in the solution. 
When added in great excess to solutions of nickel sulphate, man- 
ganous sulphide precipitates it as NiS. When added to solution of 
sulphate of zinc, it either does not precipitate it at all or only very 
slightly at ordinary temperatures. Sulphide of zinc was not found 
to precipitate manganese sulphate solution. 
As the result, then, of the observations and experiments which 
have been recited I was led to believe that the principal agent in 
the comminution of the mineral matter found at the bottom of both 
deep and shallow seas and oceans is the ground fauna of the sea, 
which depends for its subsistence on the organic matter which it 
can extract from the mud. 
In order to fit them for collecting their nutriment in this way the 
animals have been fitted with different forms of masticating or 
milling apparatus, so as to thoroughly deal with the matter 
which they pass through their bodies. It has been shown that 
most silicates are decomposed to a certain extent when ground or 
pulverised under water ; so that the mere mastication of the sand or 
mud in presence of pure water would have a decomposing action on 
the silicates which it contains. This action is much assisted, in the 
case of marine animals, by the fact that the water which they pass 
through their bodies along witb the sand is charged with sulphates. 
These are easily reduced to sulphides by the action of the organic 
matter of the secretions of the animals. The resulting sulphide at 
once suffers double decomposition with any oxide of iron or man- 
ganese which is present as such in the mud, or may be being 
set at liberty from silicates under the decomposing influence of 
trituration under water. The sulphides of manganese and iron so 
formed are in course of nature extruded by the animals, and if 
exposed to the sea water on the surface of the mud are quickly 
oxidised, the manganese taking priority. The mud below the 
surface layer, in localities where ground life is abundant, remains 
blue, being protected by the oxidation of what is above it. 
