CONTORTIONS OF ROCKS, 117 



nate with a straight one. In the case of contortions, 

 the intricacy of curvature is often limited, even to a 

 space of a few feet or inches; or else contortions of 

 so many different kinds and degrees may exist in one 

 rock of no great dimensions, that it is difficult, or 

 impossible, to believe that any force which can be 

 specified should have produced such effects. But 

 these difficulties will be considered hereafter. 



There is one peculiar circumstance sometimes at- 

 tending the minuter contortions, which requires 

 especial notice; because it has given rise to the un- 

 founded notion that the rocks which are commonly 

 admitted to be stratified, also existed in the form of 

 veins. It can only happen where two rocks of dif- 

 ferent characters approximate; and I shall here select 

 two examples from different cases, because they will 

 serve to explain all similar appearances. Full details 

 of two particular instances of these have been given 

 in the account of the Western Islands and in the 



A 



Geological Transactions. 



At the points of flexure in an alternation of quartz 

 rock and argillaceous schist, or of any two rocks dif- 

 fering in their degrees of flexibility, the lamina of the 

 soft rock is sometimes so protracted and attenuated 

 as to assume the form of a vein for a limited distance : 

 but to mistake such an appearance for a real vein, 

 requires a degree of incapacity, inattention, or pre- 

 judice, which can fall to the lot of few. Similar ef- 

 fects, but from a different cause, are observed where 

 trap rocks invade and disturb the regularity of schis- 

 tose or arenaceous strata. Minute portions of laminae 

 become compressed by the invading rock: in the case 

 occurring at Rinnoul hill, they are not only extenuated 

 till they vanish, but they even ramify. Yet no error 

 need arise, even in such a case as this; since the 



