116 ON THE FLEXURES AND 



others. Fractures are also a frequent occurrence in 

 these cases; and the union of these two appearances 

 proves, that while the bent stratum was flexible, it 

 still possessed a rigidity limiting its power of yielding, 

 within a certain range. 



Of Contortions 







Intricacy of flexure naturally leads to contortion ; 

 a term properly applicable to the appearances ob- 

 served in many rocks, and very conspicuously in 

 gneiss and in micaceous schist. Like the more vio- 

 lent degrees of flexure, these contortions have never 

 been found beyond the range of the more antient 

 strata. To convey any idea of their forms and va- 

 rieties by description, would be impossible, as the ima- 

 gination can scarcely exceed them. It is not correct 

 to say, as has been said, that these contortions, any 

 more than ordinary flexures, are limited to one of the 

 opposing lines that may be drawn on the plane of a 

 stratum ; or that they affect the vertical and not the 

 horizontal direction, as has been equally asserted. A 

 stratum may undulate according to its dip or its di- 

 rection; it maybe contorted in either line, or in both 

 at once. Nor is the imaginary limitation required; 

 as it is not necessary to limit the nature or direction 

 of the force applied. 



It is here essential to state, that while the greater 

 flexures are very extensive, whether as they regard 

 the space, or the number of strata affected, the smaller 

 are limited, and the minuter contortions confined to 

 still more narrow bounds. It is possible, for example, 

 in the case of the smaller flexures, that one portion 

 of a stratum may be bent while the other is straight; 

 or even that a bent or undulated stratum may alter- 



