242 



Scientific Geology, 



Heat, likewise, in the same manner, and if it be sufficiently powerful, 

 by producing also a crystalline arrangement of the materials, will 

 harden them into stone. Now in the case of the red sandstone, all 

 these causes may have conspired to effect its consolidation. The ex- 

 istence of beds of limestone in this formation, and of carbonate of 

 lime diffused through some varieties of the shale and even of the 

 coarse conglomerates, shows that deposition from chemical solution 

 in water, was one of the important agencies concerned in its produc- 

 tion. The inclined position of the strata, as well as the character of 

 the organic remains, show that these rocks have been elevated from 

 beneath the water, and of consequence have been, at least in part, 

 hardened by dessication. And the presence of trap rocks in the 

 midst of the formation, not to speak of other proofs of igneous action, 

 demonstrates the agency of heat in its consolidation. 



It will naturally be enquired, how the red color, so characteristic 

 of the most important varieties of this rock, could have been pro- 

 duced. Uundoubtedly it proceeds from the red oxide of iron, which, 

 in some way, has been diffused through the mass. But whether heat 

 or water was the agent employed, may be doubtful. We find on 

 breaking open the fragments in the conglomerates, that the smaller 

 ones are penetrated throughout by this coloring matter ; while the 

 larger ones are colored only to a certain depth. (See No. 143.) 

 Now, has the iron actually penetrated these nodules, or has water or 

 heat changed the iron, which they originally contained, into the pe- 

 roxide ? The latter supposition appears to me most probable ; and 

 though air and water might possibly produce such a change to some 

 extent, yet I think we must call in the agency of heat to explain the 

 very thorough manner in which some of the finer sandstones of this 

 group, have been colored red. For I doubt whether air and water 

 can do much in this process, unless they also produce incipient de- 

 composition. 



In another place I have advanced an hypothesis to explain the 

 manner in which such sudden and numerous alternations of the 

 coarsest and the finest materials in this rock may have been produced ; 

 viz. by the flux and reflux of mighty deluges, caused by the elevation 

 of mountain chains in various parts of the globe. Some of these 

 waves may have resulted from the elevation of the strata of the older 

 rocks on which the sandstone rests unconformably : for the strata of 

 the former are much nearer to vertically than those of the latter ; and, 

 therefore, must have been raised before the deposition of the sand- 



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