Ch. XV.] OF THE PRIMARY ROCKS. 347 



this rock, at some points, by mineral gradation, but also, as 

 at the Logan Rock, in Cornwall, united by large crystals of 

 felspar, which are imbedded partly in the granite and partly 

 in the vein ; and, in like manner, the granite-veins in the 

 slate, though frequently divided on each side by open lines or 

 seams, resulting from the action of the elements, yet, in very 

 many instances, the vein and the slate adhere so strongly 

 together that they cannot be accurately separated by the 

 hammer ; and appear to pass so gradually into each other, 

 that a difference of colour is the only distinguishing character; 

 and even this is sometimes, as at the junction of the main 

 mass of granite and of slate, so indistinct that we cannot see 

 where the one begins and the other ends. Not only so, but 

 the vein and the slate exhibit the same phenomena at Bunawe, 

 in Scotland, as the vein and granite do at the Logan Rock. 

 " Although the granite-veins," says Macculloch, " sometimes 

 run through the schist in a distinct form, just as they do in 

 the junction of Loch Ranza, yet in many places they are 

 intermingled with it in the most remarkable manner; 

 crystals of hornblende may be observed shooting far into the 

 body of the schist, so as to render it often difficult to assign 

 the limits of each rock, and in a less degree, the quartz and 

 felspar of the veins exhibit the same appearance." * 



Now these facts do not proclaim the disturbance of a 

 sedimentary rock by another of a totally different nature; 

 they rather suggest the idea that these rocks are of a similar 

 composition, and have been formed in the same manner. In 

 the case of granite and gneiss this suggestion would not 

 appear so startling, but in the case of granite and slate it 

 carries an air of absurdity, according to the notions generally 

 entertained of clay-slate. Let us, however, instead of using 

 a term so indefinite as clay-slate (and so inappropriate, as 

 far as the Cornish schistose rocks adjacent to granite are 

 concerned), rather regard these slates as compact felspars, 



* Geol. Trans, vol. iv, p. 120. 



