Wale 53. | CONCRETIONS IN THE LOWER COAL-MEASURES. 51 
On the sulphuretted hydrogen meeting with the ferric oxide 
present in the surface-layer of the blue muds, the following reaction 
SOCCULES 2—— 
(4) Fe,0,+3H,S=2 FeS+S8+3 If,0. 
By subsequent pressure these muds may become shales, and at 
the same time the ferrous sulphide and sulphur become iron-pyrites, 
the other product being calcium-carbonate. This reaction was 
shown not to take place if the material was boiled or sterilized. 
The authors just quoted also mention that Prof. Andrussow, after 
exploring the Black Sea, found much sulphide of iron and sul- 
phuretted hydrogen beyond the 100-fathom line, the muds at greater 
depths consisting principally of calcium-carbonate. 
M. J. M. van Bemmelen, in a paper on ‘The Composition of the 
Acid Soils in Dutch Alluvial Districts,’ gives an account of the 
changes which take place in clay-soil under the influence of brackish 
or sea-water and decomposing vegetable matter. The ground is first 
covered with reeds, and saturated with water containing calcium- 
sulphate; alter a time air becomes excluded from the soil, when 
calcium-sulphate disappears and ferrous sulphide, free sulphur, and 
perhaps a trace of ferrous sulphate, replace it; when air again gains 
access the quantity of ferrous sulphate increases, while ferrous 
sulphide and sulphur decrease, and after aération and drainage basic 
sulphates are produced. In the earlier stages of this action we 
have a close parallel to the formation of the sulphides in the Coal- 
Measures. 
I have found several instances of stagnant ponds in which were 
lying decaying fishes or other animal substances, and the mud 
surrounding them was completely blackened on account of the for- 
mation of sulphide of iron from the sulphates in the water and the 
oxide of iron in the mud. 
Bischof * placed a mineral water containing iron and sulphates 
along with a small quantity of sugar in sealed bottles. After 
about 13 months black flocks had separated. After 34 years the 
bottles were opened, and smelt of sulphuretted hydrogen. The black 
powder had nearly the composition of iron-pyrites. There was very 
little sulphate left in the water. 
These instances are sufficient to show that anaérobic organisms 
are capable of decomposing sulphates, taking the oxygen from them 
to oxidize organic matter, and at the same time producing calcium- 
carbonate and ferrous sulphide which may ultimately become iron- 
pyrites. 
I have performed a considerable number of experiments, in 
order to arrive at a conclusion as to how the nodules in the 
Coal-Measures were formed, and as it would be tedious to enumerate 
1 Recueil des Tray. Chimiques des Pays-Bas, vol. v (1886) no. 4, p. 199. 
* «Elements of Chemical & Physical Geology’ Hngl. transl. vol. i (1854) 
p. 165. 
Be2 
