DISLOCATIONS OF STRATA. 91 



we cannot ascertain, it is easy to imagine that they 

 may pass the vertical line, or become to a certain 

 degree reversed. It is very plain that, in such a 

 case, errors might he easily committed respecting 

 the relations of a particular series. If, for example, 

 any portion of a simple series were thus to he reversed, 

 so that the one part should approach towards a pa- 

 rallel direction with the other, an unreal alternation 

 would appear to exist ; or that stratum which was in 

 one place the inferior, would, in another, become 

 the uppermost. This is a case, however, which, 

 must always be difficult to prove ; although Saussure 

 and others have supposed that they have ascertained 

 examples of it. It is evidently, not only a possible 

 but a probable occurrence, when we consider the ex- 

 treme motions which strata have often undergone ; but 

 to determine it truly where it exists, must be left to 

 the sagacity and knowledge of the geologist ; as no 

 rules could be given but those which every one may 

 deduce for himself when acquainted with the pheno- 

 mena of rocks in nature. 



Contrariety of position forms one of the most inte- 

 resting and important circumstances attending on the 

 changes which strata have undergone ; not only offer- 

 ing proofs of partial and distinct seras of disturbance, 

 but presenting some of the most satisfactory evidence 

 that exists, respecting the successive changes which 

 appear in the constitution of the globe. 



The simplest case of this, perhaps, is that in which 

 approximate strata are merely inclined to each other 

 in opposing directions, and where no one is distinctly 

 placed towards the next in a reverse or unconformable 

 position. A simple series of this nature, consists of 

 beds inclined to each other in such a manner as to 

 respect one vertical line. These may converge from 



