364 ON THE APPARENT DISLOCATIONS [Ch. XV. 



themselves traversed ; ancTexamples of both kinds may not only 

 be seen within a few feet of each other, but if the granite-vein 

 be branched, each ramification may be differently affected. 



But granite-veins, whilst within granite, are said to be con- 

 temporaneous, but in slate, or when equally traversing both 

 rocks, they are then doubtful. On this view, the contempo- 

 raneous quartz-veins are sometimes older and sometimes more 

 recent than some granite-veins which are of the same age, or 

 than others which are of doubtful origin : so that if there be 

 any value in this principle, it involves the dilemma that the 

 veins existed before the containing rocks, that the latter were 

 broken and fissured previous to their formation. The same 

 arguments apply to elvan-courses, for they are similarly cir- 

 cumstanced, as respects contemporaneous quartz-veins, both 

 in granite and in slate. The prevailing opinion is, that gra- 

 nite-veins and dykes have been produced at every possible 

 period since the protrusion of the granite ; and that they are 

 posterior to the stratified rocks in which they occur ; but 

 inasmuch as they are sometimes intersected by shortj crooked 

 quartz-veins which are as old as the slate, the latter must, ac- 

 cording to the rule, be more recent than the igneous rock. 



Again, what is the result of the intercourse of these quartz- 

 veins with true veins ? It is said " that they are always tra- 

 versed by them," but we do not think that this generalisation 

 has been deduced from observation ; we rather incline to the 

 opinion that it is of theoretical origin. Wherever small 

 irregular veins are contiguous to large metalliferous veins, 

 they are regarded as strings or branches ; generally they are 

 fairly entitled to this denomination ; but we have seen the lesser 

 veins extended into the substance of the larger, just as granite 

 veins are often elongations of the mass, but sometimes con- 

 tinue their course through the granite in as distinct a manner 

 as through the slate : such minute characters, however, are 

 not very visible under ground, even when an object of 

 research ; but on the cliffs and on the sea-shore, they may be 

 easily distinguished. 



