352 ILLOGICAL GEOLOGY. 



It is an established geological doctrine, that sedimentary 

 strata are liable to be changed, more or less completely, 

 by igneous action. The rocks originally classed as "transi« 

 tion," because they were intermediate in character between 

 the igneous rocks found below them, and the sedimentary 

 strata found above them, are now known to be nothing else 

 than sedimentary strata altered in texture and appearance 

 by the intense heat of adjacent molten matter ; and hence 

 are renamed " metamorphic rocks." Modern researches 

 have shown, too, that these metamorphic rocks are not, as 

 was once supposed, all of the same age. Besides primary 

 and secondary strata that have been transformed by igneous 

 action, there are similarly-changed deposits of tertiary ori- 

 gin ; and that, even for a quarter of a mile from the point 

 of contact with neighbouring granite. By this process 

 fossils are of course destroyed. " In some cases," says Sir 

 Charles Lyell, " dark limestones, replete with shells and 

 corals, have been turned into white statuary marble, and 

 hard clays, containing vegetable or other remains, into 

 slates called mica-schist or hornblende-schist ; every vestige 

 of the organic bodies having been obliterated." 



Again, it is fast becoming an acknowledged truth, that 

 igneous rock, of whatever kind, is the product of sedimen- 

 tary strata that have been completely melted. Granite 

 and gneiss, which are of like chemical composition, have 

 been shown, in various cases, to pass one into the other ; as 

 at Yalorsine, near Mont Blanc, where the two, in contact, 

 are observed to " both undergo a modification of mineral 

 character. The granite still remaining unstratified, be- 

 comes charged with green particles ; and the talcose gneiss 

 assumes a granitiform structure without losing its stratifi- 

 cation." In the Aberdeen-granite, lumps of unmelted 

 gneiss are frequently found ; and we can ourselves bear 

 witness that on the banks of Loch Sunart, there is ample 

 proof that the granite of that region, when it was mol- 



