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under the conditions above described, it is important to keep in 

 view the fact of the diffusion of this compound through many of 

 the strata as a general constituent, and the frequent preservation, 

 even in layers of the ore, of the lamination of the contiguous 

 rock. The supposition of its being a chemical deposit formed 

 from springs charged with carbonic acid, and holding Proto-Car- 

 bonate in solution, is evidently inconsistent with these conditions, 

 and not less so with the fact of the great horizontal extension of 

 individual beds of ore and inrvpregnated shaly rocks. 



In view of these various considerations it may be con- 

 cluded : — 



First, That throughout the coal measures and other groups of 

 rocks above mentioned, as well in the portions containing coal 

 and diffused vegetable and animal matter as in the barren parts, 

 the original sediment was more or less charged with Sesquioxide 

 of Iron, and 



Second^ That this Sesquioxide, 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 and 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 reduc- 

 ing agency of the Carbon and Hydrogen, as they separate in their 

 nascent state from the organic matter, is capable, as we know, of 

 converting certain sulphates into sulphurets, and even more 

 readily of transforming the Sesquioxide of Iron into Protoxide. 

 The latter change would doubtless be favored by the affinity of the 

 Carbonic Acid present in the mass, for the Protoxide as formed, 

 and in this way the sesquioxide 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 Sesquioxide of Iron and organic matter, we have a 

 simple explanation of the general conversion of this oxide into 



