102 DISPOSITIONS, FRACTURES AND 



the stratum, and by the direction in which he is con- 

 sequently compelled to seek that part which has dis- 

 appeared from the line of his progress. But there is 

 a real distinction of this kind ; since if, for example, 

 we assume a series which is elevated at a high angle, 

 and trace it from above downwards along its plane, 

 the separated portion, in such a case of fracture, may 

 either be elevated above, or depressed below, that 

 part which it has quitted. Appearances of this na- 

 ture serve to give some insight into the place, at 

 least, of the agents or forces by which the fractures 

 have been produced. In the case of vertical strata 

 which have been broken and shifted, it is evident 

 that the motion must be horizontal ; while, in hori- 

 zontal strata, the change of place can be considered 

 as an elevation or a depression, only as it relates to 

 the progress or position of the miner. 



As it has been shown that the changes of position 

 displayed by the stratified rocks have occurred at 

 different periods, so it is certain that fractures and 

 shifts belong also to different seras. This is proved 

 without difficulty, by finding that one of these inter- 

 sects the other where two occur together ; while even 

 more than two are not unfrequent. But we must 

 remain content with knowing this bare fact ; as no 

 criterion has been discovered by which it can be as- 

 certained at what period any slip took place, or what 

 distance of time has intervened between successive 

 events of this nature. 



The circumstance of fracture proves that the rocks 

 which have thus been shifted, had acquired their in- 

 duration and rigidity before the slides took place ; 

 and as the fact of curvature shows that the rocks 

 affected in this manner were then flexible, it has been 

 argued that curvatures are necessarilv of a more re- 



