346 ON THE APPARENT DISLOCATIONS [Ch. XV. 



only render it probable that the brecciated, like the con- 

 glomerated, structure may occur in rocks of every descrip- 

 tion, being perfectly independent of the modes in which the 

 materials of such rocks were produced and accumulated. 



Having enquired into the nature of the angular and glo- 

 bular concretions of rocks which impart a fragmentary ap- 

 pearance, we are the better prepared to enter on the examin- 

 ation of the phenomena at the junction of granite with 

 slate : here also we shall find occurrences of a similar nature 

 in the detached portions of granite and of slate which are 

 respectively enveloped in the main mass of each of these 

 rocks, but they are farther complicated by the presence of 

 granite- veins traversing the slate; a convincing proof, ac- 

 cording to the prevailing theory, that the latter rock has been 

 rent and fissured by one or more convulsions. 



Granite-veins are supposed to belong to different periods, 

 because they sometimes intersect each other ; and it is pre- 

 sumed that the oldest must be those that are connected with 

 and are in continuation of the main mass of granite, because 

 they appear to have been formed at the time of the protrusion 

 of the granite through the slate in a state of igneous fusion ; 

 whilst the newer ones must be those which not only traverse 

 the slate, but also penetrate the granite in a distinct and 

 regular course, indicating that they have been injected since 

 the consolidation of the granite. But even on this simple 

 view of the subject, and admitting that the slate, in a soft 

 and yielding state of semi- fusion, could have been broken 

 and separated in every possible direction by a mass of 

 melted granite, so that in some instances, as at Cape Wrath, 

 in Scotland, the veins should far exceed in quantity the 

 stratum that is penetrated ; yet, even after every allowance of 

 this kind, it is difficult to explain the fact, that the individuals 

 of each set of veins not only intersect and heave each other 

 in the most promiscuous manner, but the same thing happens 

 between the veins of distinct kinds. Again, we not only 

 find granite-veins within granite, intimately connected with 



