50 MR. H. B. STOCKS ON THE ORIGIN OF CERTAIN [Feb. 1902, 
the conditions under which it was produced in a delta or on a sea- 
shore. Huge forests grew out into the shallow water with roots 
in the mud, and a mass of decaying vegetable matter formed a. 
swamp or morass. It is probable also that a certain amount of 
animal matter was present, derived from decaying fish and other 
sources: the result would be the solution of some of the organic 
matter in the water, and consequent absorption of the oxygen in 
solution, so that further decay must have taken place under 
anaérobic conditions. That decay can take place under anaérobic 
conditions has been abundantly proved by the action of the so- 
called ‘septic’ tank, which is a part of the modern methed of 
sewage-treatment. In a closed tank, by the action of anaérobic 
organisms, not only are albuminous and other easily decomposable 
organic matters destroyed, but such stable materials as paper and 
other forms of cellulose are likewise broken down, with the pro- 
duction of carbonic acid, hydrogen, and marsh-gas in large quantities, 
together with a humus- like substance. ‘These , products: are the same 
as those that accompany coal; and therefore it 1s reasonable to 
suppose that coal was produced in a similar way, though not so 
rapidly, as the conditions were not so favourable. 
As practically all natural organic decay is brought about by the 
agency of bacteria, coal may be said to have een produced by 
bacteria. Whether this assumption be correct or not, it is hardly 
to be doubted that bacteria were at work during the Carboniferous 
Period, and that they brought about then changes similar to those 
effected through their agency at the present time. The magnitude 
of these changes bas not been fuily realized as yet by geologists. 
The action of anaérobic organisms is a very peculiar one, and 
results in some rather unexpected changes. In sewage, the action 
of these bacteria may be'studied very clearly. Two of the almost 
constant accompaniments of sewage are a foul smell and a black 
mud: the smeil is due to sulphuretted hydrogen and volatile 
organic matter, and the mud. is black, owing to the presence of 
ferrous s sulphide ; these are produced by anaérobic organisms. Such 
organisms are not only to be found in sewage, but they are present 
ape where. 
r John Murray & Mr. Robert Irvine, in a very interesting 
eae on oceanic deposits, give a full account of the blue mud which 
exists on all coasts bevond the 100-fathom line, and state that the 
colour of the mud is due to organic matter and ferrous sulphide, 
the latter being produced by the destruction ef organic matter by 
bacteria, and the reduction of the sulphates in the sea-water.' 
The changes which take place are shown in the following equa- 
tions :— 
(1) RSO,+2C=2C0,+RS, 
where R is an earthy metal. 
(2) RS+2C0,+H,0=H,S+RCO,,.CO,, 
(3) BS+RCO,.CO,-+H,0=2RCO,+H,8 : 
i SP roe: Roy. Soc. Edin.:vol. xvii (1889-90) p. 93, & shee ‘ Deep- 
Sea Deposits’ (1891) pp. 254, 255. 
