BY W. A. MCLEOD, B.A., B.SC. 87 



The bistorj and chemical changes involved present a most 

 interesting study. ISeglecting all the complicate processes 

 resulting in the formation of wood from the ingredients of 

 the soil and air, the most important question that presents 

 itself is : " How has a piece of wood become almost totally 

 changed into iron pyrites, that is, a compound consisting of 

 iron and sulphur, in the proportion of one atom of iron to two 

 atom of sulphur ? " 



It is a well-known fact that iron pyrites can be precipitated 

 from a solution of sulphite of iron by organic matter, and 

 also from the higher sulphate of iron by carbonates, and it 

 is most probably by the former reaction that this specimen 

 was replaced. The wood, being organic matter, would be 

 the precipitating agent, but there remains the presence of 

 the lower sulphate of iron to be accounted for. This sub- 

 stance is often formed by the reverse process of that above 

 described, that is, when iron pyrites is exposed to the action 

 of air it becomes oxidised into ferrous sulphate, the conditions 

 here being purely oxidising, and in the former case reducing. 

 In many mining districts the waters are largely charged with 

 this sulphate, and frequently large stalactitic crvstals are 

 obtained from the roofs of workings and drives. Some such 

 occurrence probably caused the water percolating through the 

 drift in which the piece of wood had become embedded to 

 become charged with sulphate of iron which, on coming in 

 contact with the wood, was reduced and iron pyrites was 

 formed, which gradually took the place of the organic matter 

 consumed in the reduction process. From the strong con- 

 trast between the upper and lower portions and from the 

 sharp divisional line, it would appear that the wood had been 

 lying loosely on a deposit of drift containing fine quartz, 

 grains of subangular character, and that the lower half had 

 been |;>recipitated owing to the presence beneath the wood of 

 perhaj)s decaying organic matter, and so had enclosed particles 

 of the drift on which it was formed. 



After these changes were completed, the specimen was 

 altered in shape by physical agencies, as is evinced by the 

 rounded water-worn character of the lower and upper 

 portions. The original drift was probably cut into, and to a 

 greater or less extent removed by the agency of water, and 

 the accompanying attrition rounded off any sharp corners, 

 giving a smooth, round aspect to the specimen, and finally 

 the specimen was deposited in the locality where it was dis- 

 covered. 



It must be remembered that this short historical sketch 

 only presents what seems the most plausible theory which 

 has been presented by chemists and geologists to explain 

 such occurrences. 



