Volcanos. 1 35 



tinents and mountain ranges, with all the minor phenomena of 

 inclined and distorted strata, dikes, veins, faults, &c. which it is 

 one of the chief objects of geological inquiry to account for. 



" This chapter commences with the. remark that the arena- 

 ceous and sedimental strata, which compose the major part of 

 the surface of our continents, are found to assume a great degree 

 of inclination, and more irregularities of position, as we approach 

 the chains of mountains, or lines of maximum elevation and dis- 

 turbance. They, however, almost universally lean against mass- 

 es of crystalline rocks, which form the geological axis of every 

 mountain. Of these rocks, some are stratified, or rather have a 

 laminar structure, as gneiss, mica-slate, &c, and show marks of 

 the action of some violent force upon them, in their repeated 

 flexures, cracks, and highly inclined position ; others are unstra- 

 tified, (granite, syenite, porphyry, serpentine, diallage-rock, and 

 greenstones, &,c.,) and usually underlie the others, or cut through 

 them in the manner of immense dikes. The latter are supposed 

 by the author to be portions of the subterranean crystalline bed, 

 protruded by inferior expansion, sometimes in a state of partial 

 liquefaction, at others as a solid mass, through a longitudinal cleft 

 broken across the superficial strata. The laminated crystalline 

 rock^, which formed the lower portion of these strata were 

 forced likewise through the fissure by the tremendous friction of 

 the rising mass, and, during this process, were folded into re- 

 peated doublings, like those produced in a bale of cloth or linen, 

 by a powerful pressure, acting nearly in the direction of its lay- 

 ers. In general, the central axis of unstratified crystalline rock, 

 will appear like a vast dike intruded between the replicated 

 schists on either side ; at others, these protruded strata will still 

 cover the axis like a mantle. Where the temperature of the 

 exposed parts of the crystalline axis was intense, a superficial 

 intumescence may have taken place, the liquefied matter over- 

 spreading the edges of some of the overlying or protruded stra- 

 ta, and thus giving rise to the appearance of secondary granites, 

 syenites, porphyries, &c. Portions of lava will also be injected 

 between the folds of the lower schists ; and into any crevices or 

 fractures formed in them. At the same time, the upper strata 

 recede in a lateral direction, from the axis of elevation, slipping 

 down the inclined planes of their stratification, by the influence 

 of gravity, and become also more or less bent and folded togeth- 

 er, owing to the resistance opposed to this subsidence, by the in- 

 ertia of their distant unelevated parts. Curvatures and replica- 

 tions could, however, only take place where the strata were in 

 a semi-solid state, or where the peculiar structure of the rock 

 was favourable to the partial mobility of its parts ; and this ap- 

 pears to have been particularly the case with the laminar and 



