274 ON THE TRANSMUTATION OF ROCKS, &c., 



ceivablc notions of such a rock having been formed simply by 

 igneous fusion, and that, therefore, water must have been an 

 agent of considerable importance. 



About nineteen or twenty years ago a controversy took place 

 between some continental geologists as to the origin of the beau- 

 tiful marbles of Italy. Near the Lake of Como exist certain 

 rocks that have been denominated Gneiss, and this has been 

 adduced as a proof that such gneiss and the marbles also, are the 

 result of the transmuting power of granite. Now, in the Italian 

 peninsula, no sedimentary formations are known to exist of older 

 epochs than those of the Jurassic and Cretaceous and Upper 

 Tertiary. 



M. Boubee asserted that older rocks did exist concealed 

 under the deposits named, and that M. de Collegno and others 

 who took the same view as he did were wrong. He maintained 

 that heat could not permeate so as to change by igneous trans- 

 mutation any rock thicken than 6 or 7 feet ; and that, therefore, 

 masses from 100 to 1000 feet thick could not be so changed. 

 He concluded, then, that the Jurassic limestones (which belong 

 to the same category as those of Greece), were altered by slowly- 

 acting, long-continued, electric and chemical molecular forces. 

 But I must say, that M. Boubee does admit occasional examples 

 of transmutation by heat alone, and that is, I presume, all that 

 the advocates of that doctrine require. They do not, and they 

 cannot ignore other agencies. 



The fact that the impressions of fossil plants occur often in 

 highly silicified beds, proves that a change by imbibition of silica 

 may occur, set free by heated waters or vapour. 



No one could pretend that any plant could leave a cast in 

 such hardened rock as this in which a cast of a Lepidodendron 

 from Sofala appears, or of this in altered shale from Canooiia. 

 It is absurd to suppose that the silicated rock was in a plastic 

 state when the plant became enveloped in it. 



On the other hand, it cannot be denied that lime, iron, and 

 other rnetals have occasionally made their appearance in veins by 

 direct igneous emanations impregnating and coating solid rocks 

 of other kinds. And the only source that can be supposed for 

 silica so developed is from granitic rock. Silicated water at a 



