68 



the non-existence of dikes in the fine granite, while they are often 

 met with in the coarse. He states his view with some diffidence, 

 and with the qualification that the tract of fine grained granite has 

 not been carefully investigated with respect to these appearances. 

 This examination was made by us last summer ; and the result was 

 the discovery of several trap dikes, ranging between north and north- 

 west across the tract of fine grained granite; but the intersec- 

 tion of these with the coarse grained variety could not be observed, 

 nor has such intersection been anywhere noticed by us. It is quite 

 possible, however, that there may be one system of dikes in the 

 coarse granite cut off by the fine, and another system in the fine 

 itself. If the intersection does indeed occur in the manner men- 

 tioned in the above quotation, the conclusion will be forced upon us 

 that the fine granite is of later eruption than the coarse, and also 

 later than the dikes in this coarse variety. There would thus be 

 granite of two ages, and trap of two ages, in this central district. 

 We must, however, express our belief, that the discovery of trap 

 dikes traversing the fine granite for considerable distances renders it 

 extremely probable that they are continued both ways into the 

 coarse variety ; and that, while the two granites may "be of different 

 ages, the dikes are of one age and posterior to both granites. We 

 shall have occasion hereafter to refer to the age of these two granites. 

 The veins of fine granite, which are so frequently found traversing 

 the coarse granite of Groatfell, Ben-Grhnuis, and other localities, are 

 certainly cotemporaneous, formed by chemical affinities or electric 

 forces acting in some peculiar way during the consolidation of the 

 rock, and not injected from below at a later date. In many cases 

 indeed they are seen quite isolated in a granite block. Sir Charles 

 Lyell, who "himself examined a great part of Arran in 1836," 

 adopts the view set forth by Mr. Ramsay (El. of Geol., 5th ed., 

 1855, p. 590). This view he illustrates by a cut (p. 591), which is 

 slightly inaccurate, as the facts above stated will show. The fine 

 granite does not rise into mountains, co-ordinate with those formed 

 of the coarse variety ; the fine grained is actually traversed by dikes 

 of common trap through considerable distances ; and we contend 

 that evidence is wanting to prove the injection of veins of the fine 

 variety into the coarse. An error in one of Mr. Ramsay's sections, 

 at the points 5, f, is also copied into this cut, to which we shall 

 again refer. 



47. The encircling band of clay slate is succeeded on the east and 

 south by a band of old red sandstone, which, like the slate band, is 

 of irresrular breadth. It begins to overlie the slate at the Fallen 



