36 Proceedings of Royal Society of Edinburgh. [sess. 
that we referred to in the formulae given in our paper. (See vol. 
xxxvii. p. 496.) 
Professor Hartley next refers to the influence of living organisms 
reducing sulphates and forming with ferric-hydrate ferrous- 
sulphide, founding his facts upon a paper by Mr J. Y. Buchanan 
“ On the Occurrence of Sulphur in Marine Muds.” It is not 
necessary for us to further reply to this statement, as the subject 
has been dealt with, first, in a paper by Irvine and Gibson,* and, 
second, in a paper by Murray and Irvine, f showing that whilst 
manganous sulphide is rapidly decomposed by carbonic acid, 
ferrous-sulphide is stable under such circumstances ; so that whilst 
ferrous-sulphide is present in these blue muds, often in large 
quantity, manganous sulphide is decomposed by the carbonic acids 
or bi-carbonates present in sea-water, bi-carbonate of manganese 
being formed and sulphuretted hydrogen given off. 
Professor Hartley goes on to state that alga or cellulose has the 
power of decomposing sulphate of lime and producing sulphuretted 
hydrogen, and that this decomposition is effected through the 
agency of the “ bacillus amylobacter,” giving the somewhat com- 
plicated formula described by Hoppe-Seyler in 1886, by which 
methane and carbon-dioxide are produced under the influence of 
this bacterium. We do not think it necessary to criticise the 
results he refers to, as in our paper we admit and refer to the 
influence of bacteria in bringing about the changes which lead to 
the production of blue muds. Indeed, experimentally we showed 
in 1892 that sea-water containing sterilised organic matter and 
ferric-hydrate failed to exhibit the changes which in an unsterilised 
condition gave the characteristic reduction of the sulphates and the 
production of ferrous sulphide, such as occurs in blue muds. In 
Frankland’s book on Micro-Organisms in Water , page 114, is given 
a table by Russell showing the number of bacteria found in sea 
muds deposited at different depths. In mud deposited at a depth 
of 15 metres, 1 c.c. contained 245,000, whilst the water immedi- 
ately above only contained 121,000. The numbers are rapidly 
* ‘‘Manganese Deposits in Marine Muds,” Irvine and Gibson. Proceedings 
Royal Society of Edinburgh, 1890 and 1891. 
t “Manganese Oxides and Manganese Nodules,” Murray and Irvine. 
Transactions Royal Society of Edinburgh, Vol. xxxvii., Part iv., No. 22. 
