CONTORTIONS OF ROCKS. 115 



series of strata, which is only bent at one point, is 

 broken in another. As this fact is of importance in 

 reasoning respecting the causes of curvature, it is pro- 

 per to point out one remarkable instance where the 

 fracture and flexure are found co-existing at the same 

 point of curvature; the different effects arising from 

 the different nature of the associated rocks. This 

 example, already quoted for another purpose, may be 

 seen in Lunga, where argillaceous schist and quartz 

 rock are found alternating. Where the flexure is very 

 acute, the quartz rock is broken while the schist is 

 only bent ; and, in some extreme cases, fragments of 

 the former are separated and entangled among the 

 latter; facts speaking a language that cannot be mis- 

 apprehended. 



It seems to be admitted that curvatures on the large 

 scale may take place in more than one direction, so 

 that the strata shall represent spheroidal crusts, either 

 concave or convex. I am neither able however to 

 refer to any well-marked instances of this nature, nor 

 axvare that they involve any peculiarities which may 

 not easily be conceived. 



Curvatures of small dimensions are generally more 

 intricate and violent than the larger, and they abound 

 every where. It will also be found that they are far 

 more frequent in the primary and most antient, than 

 in the more recent strata; and, of this fact, gneiss 

 offers some of the most remarkable examples. It 

 must also be observed, that the parallelism of the ap- 

 proximate strata is not so well preserved in these 

 cases ; the curvatures in them differing, either from 

 the originally unequal thickness of the different beds, 

 or because, daring the period of softness and motion 

 by which these phenomena are here explained, some 

 parts have undergone a greater extension than the 



i 2 



