RELATIVE AGE OP THE GRANITES. 21 



these granite fragments been derived? From the body of 

 fine granite among the northern mountains, or from the 

 adjoining mass itself? Mineral structure does not enable us 

 to determine the two rocks are so similar. If from the 

 former source, then we must conclude that the granite of the 

 interior was elevated so as to be exposed to disintegrating 

 causes, while the conglomerate was forming; in which case 

 granite fragments ought to occur abundantly in the sand- 

 stone conglomerates ; but this is not found anywhere in 

 Arran a fact noticed by all observers. Even, here the 

 fragments occur only in close proximity to the granite itself. 

 Must we not then rather suppose that pieces of the granite 

 adjoining, when this rock was erupted in a fluid or semi-fluid 

 state, were injected among the outer strata of the conglo- 

 merate, also fused by the contact, and so became imbedded 

 in these strata only ? 



Sir Charles Lyell, in discussing the relative age of the 

 Arran granites (El, p. 720, edition 1865), favours the view 

 stated in the last sentence. Having quoted the above passage 

 from our former edition (3rd, 1864), he observes, -"I have 

 seen a similar junction in Caithness, of which Sir R. 

 Mxirchison, in 1827, and again in 1828 jointly with Pro- 

 fessor Sedgwick, has given a faithful description. Close to 

 the point of contact of certain oolitic sandstones, shales, and 

 limestones, in the Caithness cliffs, a breccia occurs containing 

 granite fragments, mixed with those of the invaded rock. 

 The granite, they say, appears as if it had been mechanically 

 driven in among the shattered and altered strata." 



This case, unknown to me till I saw it quoted as above, 

 strongly supports the view which I have taken, that the 

 imbedded fragments at Craig-Dhu form no exception to the 

 general rule regarding the Arran conglomerates. 



Relative Age of the Granites. 



13. Granite, then, occurs in Arran, in three disconnected 

 tracts, amid slates in the northern mountains, in the old red 



