DISLOCATIONS OF STRATA. 



proper place for that discussion will be found hereafter. 

 (Chap xxi.) It is sufficient to remark, that they 

 prove a series of changes, with intermediate intervals 

 of repose ; changes which have elevated in succession 

 the strata that had been once deposited in a horizontal 

 position, and times of rest permitting the formation 

 of new deposits. 



It is evident, that the variations in the appearances, 

 at these junctions of unconformable strata, may be 

 considerable; as there is no limit to the varieties of 

 position which the inferior strata may have assumed. 

 The angles at which they meet may amount to a 

 right angle: they may be infinitely small, or parallel, 

 even between those rocks which, at another point, 

 may be completely reversed; since these circum- 

 stances must depend on the discordant or regular po- 

 sition of the fundamental strata. It is plain, for ex- 

 ample, that a horizontal series of strata now deposited 

 on the Argyllshire series already described, would oc- 

 cupy every possible relative position to the same rock. 

 Thus, although a reverse position is always sufficient 

 to prove an interval of time between successive strata, 

 its absence is not always evidence of the negative. 



The simplest case only has been stated; namely, 

 that in which the superior strata are horizontal, what- 

 ever may be the position of the inferior. But the 

 superior strata are often highly inclined, while the 

 inferior are still unconformable to them. It is pos- 

 sible that, in such a case, the most antient strata may 

 be the least inclined of the two : they may even be 

 horizontal. Whatever may be the fact in this respect, 

 it is plain that the inclined state of the superior 

 strata proves that even they have been displaced 

 since their deposition; and thus it is also proved 

 that the inferior strata have been twice dis- 



II 2 



