846 THE WONDERS OF GEOLOGY. Lect. VIII. 



innumerable granite veins with which they are traversed. 

 The face of the rocky cliffs appears like veined marbled 

 paper ; and the imagination can scarcely conceive an in- 

 tricacy, or interlamination of this nature, of which a resem- 

 blance could not be found in the cliffs of Lewis.* 



From the decomposition and falling away of the sur- 

 rounding parts of the rocks near Oreby, an interesting, per- 

 haps solitary, example occurs, of a bent and detached mass 

 of gneiss, about thirty or forty feet high (Lign. 189), and 

 which forms a highly interesting and picturesque object. 



The stratified appearance of gneiss and mica-schist is 

 attributed by some geologists to an arrangement of crystals 

 of different specific gravities in horizontal planes ; their 

 subsequent softening by heat, admitting of the flexuosities 

 of these rocks ; and it is inferred that melted granite, 

 upon cooling under particular circumstances, would assume 

 a stratified appearance, analogous to that of gneiss; or might 

 even resemble the structure of aqueous sediments. 



23. Contortions of crystalline rocks. — The cur- 

 vatures and flexures of rocks, largely composed of quartz, 

 is a subject of great interest in another point of view, 

 because it bears upon the question as to the solution and 

 deposition of silex ; a process which appears to have been 

 going on in the crust of the earth from the mode of forma- 

 tion of the most ancient granitic rocks, to the deposits now 

 in progress. I have before remarked, that the appearance 

 of some of the siliceous infiltrations in the tissues of sponges, 

 ventriculites, and other zoophytes, and even in the intimate 

 structure of wood,! when seen under a highly magnifying 

 power, is that of a viscid fluid, or plastic paste, pressed into 

 the interstices of the tissue, rather than that of the per- 

 colation of a mineral solution, or of a metamorphism of 



* Western Isles, p. 193. 



■f As for example, in some of the fossil wood from Egypt and Aus- 

 tralia. See ante, p. 711. 



