CONTORTIONS OF ROCKS. 113 



being productive of correspondent undulations in the 

 surface of the land. It is scarcely necessary to say 

 that it varies, as well in the degree as in the dispo- 

 sition ; the curvatures differing exceedingly in their 

 length of radius, and being either limited to one, or 

 repeated in successive undulations, so as to present 

 points of contrary flexure. Curvatures of this exten- 

 sive nature are also found to involve a whole series of 

 strata ; extending to depths, of which the limits have 

 not been ascertained. The Coal deposits of Ireland 

 present conspicuous examples of this nature ; but the 

 most splendid and satisfactory instance in Britain, is 

 found in the natural and deep section that separates 

 the islands of Jura and Scarba. The whole series of 

 repeated strata, consisting of quartz rock, micaceous 

 schist, and argillaceous schist, is here laid bare in 

 cliffs of many hundred feet in height, and may be 

 examined with ease by those who may choose to en- 

 counter the dangers of the famed Cory vrechan. 



It does not often happen on this very large scale, 

 that the curvatures of the strata are so considerable as 

 to become coincident with those of lengthened el- 

 lipses, or that the opposite sides about the points of 

 flexure approach towards a parallel position. Exam- 

 ples of this nature have however been observed ; and 

 the consequences are sometimes such as to give rise 

 to important errors respecting the alternations and 

 relative positions of certain strata. As the superficial 

 rocks of a tract of country are often removed by the 

 consequences of that process which has been called 

 denudation, it is easy to understand how, in such 

 a case of successive acute undulations, all the points 

 of flexure at the surface may have disappeared ; 

 leaving the appearance of a succession of strata more 

 or less irregularly inclined to each other, or even, it 



VOL. i. I 



