342 On Proto-carbonate of Iron in Coal Measures. 
and diffused vegetable and animal matter as in the barren parts, 
the original sediment was more or less charged with sesquioxyd 
of iron; an 
Second, That this sesqnioxyd, in the presence of the changing 
vegetable matter with which certain of the strata abounded. was 
converted into proto-carbonate, which remained in part diffused 
through these beds, or by processes of filtration aud segregation 
was accumulated in particular layers. 
It is well known that during the slow chemical changes by 
which vegetable matter inclosed in moist earth is converted into 
lignite, or coal, both light carburetted hydrogen and carbonic 
acid are evolved, and that these gases are even eliminated from 
coal seams and their adjoining carbonaceous strata. The redu- 
cing agency of the carbon and hydrogen, as they separate in their 
nascent state from the organic matter, is capable, as we kuow, of 
converting certain sulphates into sulphurets, and even more 
readily of transforming the sesquioxyd ‘of iron into protoxyd. 
The latter change would doubtless be favored by the affinity of 
the carbonic acid present in the mass, for the protoxyd as formed, 
and in this way the sesquioxyd, would be entirely converted into 
the proto-carbonate of iron. 
Conceiving a like process to have operated on a large scale in 
the coal measures or other strata containing, when deposited, a 
mixture of sesquioxyd of iron and organic matter, we have a 
simple explanation of the general conversion of this oxyd into 
carbonate, and of the loss of the reddish coloring in which these 
materials more.or less participated. As these actions must be 
supposed to have commenced in each stratum as soon as the or- 
gatic matter contained in it began to suffer chemical change, we 
may conclude that the formation of the proto-carbonate was 
already far advanced in the earlier strata when only beginning 
in those deposited at a later period. Each layer of vegetable 
matter, as it was transformed into coal, would not fail to impreg- 
nate the adjoining beds of shale and sandstone with the proto- — 
carbonate, and thus the development of this compound was as it 
were coeval with that of the coal. 
escribed ; and indeed, it is possible“that in some strata it is not 
yet entirely finished. In this process, which finds, a,simple ex- 
planation in the combined action of infiltration and.the segrega- 
ting force, it can hardly be questioned that the carbonic acid, per- 
vading the mass of sediment, acted a very important part. ‘The 
large amount of this gas evolved from the beds of vegetable 
