318 ANNUAL OF SCIENTIFIC DISCOVERY. 



Dr. Hayes remarked that he had long been aware that the conditions 

 belonging to deposits of proto-carbonate of iron in the coal measures, are such 

 as to forbid the supposition that the compound had been deposited from 

 waters holding the carbonate of iron in solution. The view presented, which 

 refers the production of the carbonate, from the peroxide, by the reducing 

 action of organic matter undergoing changes in contact with it, harmonizes 

 with a mass of chemical facts and observations alseady accumulated. The 

 native hydrated peroxides of iron can be thus reduced to protoxide, and in 

 fact converted into proto-carbonate of iron, in the laboratory, by the aid of 

 decomposing vegetable matter. In observing this change it is always found 

 that the reducing action on the peroxide commences at the time that the first 

 steps in the decay of the organic matter are observed. Carbonic acid gas, 

 with carburetted hydrogen gas, appears at a later stage ; the protoxide of 

 iron formed being insufficient in quantity to combine with all the carbonic 

 acid which is produced. It is an essential condition in this change that 

 water, or moisture, is present ; as the organic decomposition a kind of putre- 

 faction would not otherwise take place. It is proper in this connexion to 

 state the fact that the ferruginous springs of this country rarely contain car- 

 bonate of iron dissolved. The iron salt which is present, is a crenate, origi- 

 nating from the decomposition of organic matter, in contact with ferruginous 

 earth. The crenate of iron exists only as a proto-salt ; it is soluble in water, 

 and when brought into contact with air, hydrate of peroxide of iron falls, 

 usually containing some humus, or coaly matter, resulting from the decompo- 

 sition of the crenic acid. It is not probable that the crenate can produce the 

 carbonate of iron, if oxygen is present ; but, when protected from oxidation, 

 and especially in presence of an excess of carbonic acid, the crenate may form 

 a proto-carbonate of iron, as the crenate of lime, even in the atmosphere, forms 

 carbonate of lime. 



In referring the production of carbonate of iron deposits in strata to the 

 solvent action of carbonic acid dissolved in mineral waters, any theory should 

 point out the source from whence the protoxide of iron is taken, to form the 

 dissolved carbonate, as protoxide of iron does not naturally exist. If a 

 previous reduction of other oxides of iron, by organic matter, is necessary to 

 ensure this solution, it will probably be found that crenic acid, instead of 

 carbonic acid, is the solvent. 



The explanation, as given by Prof. Rogers, becomes, therefore, not only the 

 simpler view, and strictly accordant with known facts, but it seems to be 

 necessary as a basis for the theory generally received. 



There is a point of geological interest in connection with the manner in 

 which the proto-carbonate of iron is included in the coal series, and often in 

 contact with beds of co.al. This compound, as before stated, is a hydrate 

 compound, and its varieties generally lose their carbonic acid, and become 

 peroxide by a moderate elevation of temperature ; its presence, therefore, in 

 contact with alternating beds of coal, may be considered as indicating that 

 such beds have not been subjected to heat above the temperature at which 

 the carbonate is decomposed. 



