CONTORTIONS OF ROCKS. 129 



not, for example, be found in a vertical position. If 

 again the contorted forms of these rocks are con- 

 ceived to have arisen, as well as the straight, from 

 crystallization, it is plain that the law of polarity, 

 which is in one case preserved, is in the other vio- 

 lated. In either case, the curvature of the strata 

 from actions posterior to the disposition of their con- 

 stituent minerals, is proved by evidence that admits 

 neither of evasion nor dispute. 



It now remains only to inquire respecting the 

 nature and actions of the forces which have produced 

 these effects. 



The evidences of change of place in the strata after 

 deposition, have already been stated ; and it has been 

 shown from the phenomena of trap rocks, and from 

 other appearances, that we can even form probable 

 conjectures respecting the nature and cause of some 

 of these moving powers. On these subjects there is 

 nothing further to be added in this place. 



It is not easy, however, always to specify the 

 manner in which these forces have acted in producing 

 the curvatures of strata. In some cases, it may be 

 imagined that the mere force of gravity, acting on a 

 flexible mass unequally supported, may have been a 

 sufficient cause ; or, that under the same circum- 

 stances, strata may have been bent by the action of 

 those subterrene expansive forces which have elevated 

 the coral rocks of the Pacific high above the level of 

 that sea in which they were produced. But the cases 

 of highly undulated strata with alternate points of 

 contrary flexure, appear to require a lateral pressure 

 exerted on highly flexible strata, in a manner of 

 which we can form no distinct conception. Still less 

 can we assign the precise action of forces capable of 



VOL. i, K 



