Ch. XIV.] OF THE STRATIFIED ROCKS. 311 



If, then, granite has been brought into contact with the 

 .stratified rocks in a state of incandescence, what effect has it 

 produced thereon ? If its action has been analogous to that 

 of trap, " it must have altered their texture ; and this alter- 

 ation must exhibit every intermediate gradation between 

 that resulting from perfect fusion, and the slightest modifica- 

 tion which heat can produce." 



Now, what is the fact ? The primary slates, at their junc- 

 tion with granite, have generally a different appearance from 

 those parts of the rock that are more distant j and they, in 

 such situations, very commonly possess a finer texture, and a 

 greater degree of hardness : but here the analogy with the 

 altered condition of the secondary strata next trap terminates ; 

 for a closer scrutiny will show, that the difference, in the case 

 of the primary slates, is not such as heat alone could effect, 

 it has not arisen from any modification of induration or 

 fusion, but by a chemical change in the proportions, or the 

 nature of their constituent parts : and this circumstance not 

 only applies to the schistose rocks, but in very many cases is 

 participated in by the granite. Refer to the seventh chapter, 

 describing the nature of these rocks at their junction, where 

 several examples are minutely detailed. Can it be supposed, 

 however potent caloric may be to change clay-slate into 

 flinty slate, and sandstone into jasper, that it can convert one 

 earth into another, alumina into silica, as indicated by the 

 quartzose nature of clay-slate and other schists, when in con- 

 tact with granite ; or lime into silica, as exemplified in the 

 limestone of Glen Tilt, where, as it approaches the granite, 

 " its crystalline texture disappears, and it gradually assumes 

 the characters of hornstone, effervesces slowly with acids, and 

 gives, on analysis, a large portion of siliceous matter." 



This transmutation of one earth into another, may not 

 present any serious difficulty to those who can give credence 

 to the hypothesis concerning the dolomization of limestone : 

 but it is to be hoped that geologists will not sanction an 

 opinion so utterly at variance with the principles of chemical 



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