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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 

 organic 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. 



The gathering of the diffused Proto-Carbonate into bands and 

 courses of ore began no doubt as soon as the production of this 

 compound had made some progress, but it probably continued 

 until long after the completion of the chemical changes above 

 described ; and indeed, it is possible that in some strata it is not 

 yet entirely finished. In this process, which finds a simple 

 explanation in the comhined action of infiltration and the segre- 

 gating force^ it can hardly be questioned that the carhonic acid, 

 pervading the mass of sediment, acted a very important part. 

 The large amount of this gas evolved from the beds of vege- 

 table matter undergoing change, would impart to the water of the 

 adjoining strata the power of dissolving the diffused Proto- 

 Carbonate, which, being then carried by infiltration through the 

 more porous beds, would accumulate above and within the close 

 argillaceous or shaly layers, forming in some cases bands of 

 rock ore, in others courses of nodular and plate ores. Of these, 

 the former would seem to have, resulted from the accumulation 

 by gravity of the dissolved carbonate in the substance of sandy 

 shales near the upper limit of the more impervious beds, while 

 we may regard the latter as having been collected in all direc- 

 tions from the general charge of Proto-Carbonate accumulated 

 in the argillaceous mass, its mobility in the dissolved condition 

 greatly aiding the gathering process of the segregating force. 



