352 ON THE APPARENT DISLOCATIONS |Ch. XV. 



described the mutual interference of limestone and schist with 

 each other at Gow's Bridge, in Glen Tilt, he remarks, that 

 " it is evident, that both the prolongation of the limestone 

 and that of the schist bear a great resemblance to the veins 

 which, in the case of granite, may be traced from a mass of 

 that substance into the neighbouring rocks : yet there is no 

 doubt that both these rocks are stratified. I have observed 

 the same appearance in clay-slate, and it is frequent in 

 the islands of Scarba and Jura, where this substance alter- 

 nates with quartz-rock, and where both rocks are greatly 

 contorted. A more remarkable example occurs in a rock 

 which constitutes one of the numerous beds of which Schi- 

 hallion is composed. This rock is a mica-slate, containing 

 imbedded fragments of granite and of quartz-rock, often of 

 considerable magnitude. The larger fragments of quartz- 

 rock are sometimes partially split at right angles to its 

 lamellar structure, and these fissures are filled with the sub- 

 stance of the mica-slate, putting on the same pseudomor- 

 phous appearance of a vein. I have found similar veins of 

 red sandstone in the limestone of Arran, and they have also 

 been seen in trap : thus, at Kinnoul, greywacke schist is pro- 

 longed into ramifying veins in the interstices of a trap rock 

 by which it is broken and disturbed. * And, lastly, the con- 

 tortions of argillaceous schist in Isla are very great, and 

 sometimes they are elongated into the body of the quartz- 

 rock : " The appearance is so like that assumed by veins, 

 that it is not surprising if it has sometimes misled observers." f 

 Now we frankly confess that, in this case, as in that of dis- 

 criminating between the layers of granite and the strata of 

 primary slates, we have not only lost our way, but cannot 

 discern it even when thus pointed out ; for we have looked 

 again and again, and cannot perceive that Nature has made 

 any distinction between granite-veins and slate-veins ; we 

 can only see, in this peculiar form of matter, elongated por- 



* Geol. Trans., vol. iii. p. 279. 



f Western Isles of Scotland, pi. xxii. fig. 5. 



