WITH ANTICLINAL AXES AND FAULTS. 



345 



that of the rocks from which it is directly derived, is due to what 

 is usually termed volcanic action. 



Deferring my objections to these views to a later head, I would 

 venture to throw out a suggestion as regards the evolution of 

 nitrogen from these and other thermals, which appears to me not 

 unworthy of consideration. Admitting, with Dr. Daubeny, what 

 I think extremely probable, that this gas, as it appears in ther- 

 mals, is but a residuum of the atmospheric air which, conveyed 

 from the surface to the source of heat below, has there been par- 

 tially or entirely deprived of its oxygen, I would inquire, whether 

 the composition of the rocky beds through which the atmosphere 

 is thus conducted is not itself capable of explaining the result. 



The limestone For. II, and the slates forming a part of For. I, 

 always contain more or less protoxide of iron and carbonaceous 

 matter, even after long exposm-e to the action of the weather. 

 Where freshly taken from a new excavation at some depth, the 

 latter rocks abound in the protoxide, and the limestone exhibits 

 nearly all its iron in that-stage of oxidation. It would therefore 

 seem probable, that these and the other strata deposited beneath 

 the Appalachian sea, contain, at great depths, this oxide to the 

 exclusion of the sesquioxide. Looking to the large accumula- 

 tion of the latter in a hydrated state, segi-egated in various parts 

 of these several formations, it is not unreasonable to infer an 

 even greater proportion of the protoxide in the deeply bm'ied 

 strata than would correspond to the whole quantity of iron com- 

 bined in the rock above. That the presence of diffused organic 

 matter, such as we know to have been deposited with the other 

 materials of the strata, would secm*e the protoxide from further 

 oxidation, while still in contact with the waters of our gi-eat Ap- 

 palachian ocean, is a result in harmony with what we witness 

 in our present seas, and with the known chemical relations of 

 the substances concerned. Conceding, then, the existence of the 

 protoxide in due proportion in these older formations, and imag- 

 ining the air to obtain access to these strata at a depth at which 

 the temperature is sufficiently high to cause a rapid absorption 

 of the oxygen by the protoxide, we should have a large amount 

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