DISLOCATIONS OF STRATA. 105 



rock which forms the cementing substance, consisting 

 of fragments of the original ones united by infil- 

 trations of quartz. 



In terminating this description of the appearances 

 which attend the fractures and shifts of strata, it is 

 proper to inquire respecting the truth of a remark 

 which has been made by philosophers of high reputa- 

 tion, namely, that they are more frequent among the 

 primary than the secondary rocks. I believe it will 

 appear, on an unbiassed investigation, that this is not 

 the fact ; neither is its existence necessary for the 

 support of the arguments in aid of vyhich it appears 

 to have been brought forward. Contortions and 

 flexures, it may be admitted, are most frequent and 

 extensive among the most antient rocks ; but as- 

 suredly none of these can be said to exhibit the 

 derangements under consideration, in a degree supe- 

 rior to some of the latest deposits, to the coal strata, 

 for example. But this distinction is in itself curious, 

 and even perhaps more valuable in argument than 

 the imaginary statement here contradicted ; as it 

 proves, that although both kinds bear marks of dis- 

 placement and force, they have yielded to it according 

 to important differences, either in their original con- 

 stitution, or in the accompanying circumstances. 



The proofs of elevation of the strata given at the 

 commencement of this chapter, are sufficient to ac- 

 count for the occurrence of fractures and shifts ; and 

 whatever causes may be assigned for the one, they are, 

 with certain modifications, applicable to the other. It 

 remains, however, to consider what further arguments 

 these phenomena afford towards the existence of 

 motion among the strata. 



The bare circumstance of a separation existing 

 between the ends of two sets of strata, in the order 



