CONTORTIONS OF ROCKS. 123 



consistent with fact; and that, even on the great scale, 

 the laws of crystallization are consistent. In the 

 island of Coll, there is a vein of graphic granite of 

 great dimensions ; and, throughout the whole of it, 

 the felspar, however interrupted by the intermixture 

 of quartz, preserves a common polarity; proving that 

 the entire mass has been subject to the simple geo- 

 metric rule which determines the form of the funda- 

 mental rhomb of felspar. But enough of this gra- 

 tuitous hypothesis. 



In examining the probable cause of flexures, there 

 are two points to be considered, namely, the capacity 

 of the rock to admit of bending, and the power by 

 which this effect was produced. 



The present rigidity of the strata obliges us to seek 

 for facts to prove that they have not always been in 

 that state, and I shall here enumerate those which 

 bear on that question. It has elsewhere been shown 

 (Chap, xii.) that water is contained, in perhaps all 

 rocks, and, in many, in considerable quantity; being 

 so loosely united, at the same time, as to be readily 

 dissipated on exposure to the air. Thus minerals, 

 rigid and hard as glass in our cabinets, are often 

 flexible and soft in their native beds ; a case which, 

 in my own experience, occurs in asbestos, sahlite, tre- 

 inolite, and chalcedony, and which is said also to happen 

 in the beryl. It is not unlikely that it will be found 

 far more common, when mineralogists shall themselves 

 collect their specimens from nature, and not from the 

 repositories of dealers. It is not unreasonable to 

 conclude that a state which belongs to the simple 

 minerals, may also belong to their compounds. It is 

 even more probable, when we consider that the union 

 of heterogeneous parts would more readily admit of 



