Vol. 52.] GRANOPHYRES OP STRATH (sKYe). 327 



granophyres seems to point to a distinct separation between them 

 in respect of time and of the circumstances attending intrusion, and 

 the contrast between the xenoliths of the two types decidedly 

 enforces this reasoning. The portion of the acid magma first 

 intruded appears to have merely enclosed fragments derived from 

 the bounding walls, as many other igneous rocks have done in this 

 and other districts. The main body of the granophyre-magma, which 

 followed perhaps after some interval of time, has taken up foreign 

 material amounting to fully | of its own bulk, derived, not from 

 the bordering rocks, but from a gabbro probably at a consider- 

 able depth beneath. Herein, too, this latter case differs from the 

 examples already cited from other districts. At Barnavave, where 

 the evidence seems to be singularly complete, the phenomenon is 

 essentially a ' contact ' one. At Carrock Fell, owing to special cir- 

 cumstances upon which I have remarked elsewhere, the dissolution of 

 the derived fragments has proceeded much farther than in tbe Irish 

 example, but the broad relations are the same. The modification 

 of the granophyre is confined to the neighbourhood of its contact 

 with the gabbro, and disappears rapidly as we recede from that 

 contact. In the instance now described in the Strath district, on 

 the other hand, the abundant foreign material has been taken up 

 prior to the intrusion of the magma into its present surroundings ; 

 has been distributed with some approach to uniformity prior to or 

 during the intrusion ; and, except for the relics described above, 

 has then been absorbed into the granophyre-magma. The whole 

 mass of each intrusion, excluding the fine-textured non-granophyric 

 portions, has the same general characters throughout. 



A question of general interest naturally arises from a consideration 

 of this case. If the caustic action of the acid magma had been from 

 any cause more energetic, and had sufficed to destroy the relics of 

 gabbro as completely as has been effected at Carrock Fell, it would 

 have been impossible (without careful and specially directed search) 

 to detect any evidence of the incorporation of foreign material. Is, 

 then, this factor an important one to be taken into account in 

 discussing the origin of igneous rocks in general ? Prof. Sollas, 

 Dr. Johnston-Lavis, 1 and some other geologists would probably 

 answer this question in the affirmative : I refrain from expressing 

 any opinion. 2 The facts detailed above admit of obvious application 

 to the problem ; but it may be urged on the other hand that, were 

 complete absorption of xenoliths to modify the composition of a 

 rock-magma a frequent occurrence, cases of incomplete absorption 

 such as that here described should be more common than they 

 appear to be. 



1 Geol. Mag. 1894, pp. 47-48, 252-254; 'Natural Science,' vol. iv. (1894) 

 pp. 134-140. Comp. A. von Lasaulx, Neues Jahrb. 1870, p. 713. 



2 Prof. Brog:ger has recently stated with much cogency the argument against 

 the hypothesis of Kjerulf, Michel Levy, and others, which supposes that granite- 

 intrusions have in general ' assimilated ' large portions of the neighbouring 

 solid rocks. See 'Die Eruptivgesteine des Kristianiagebietes,' pt. ii. pp. 116, 

 et scqq., Videnskabsselskabets Skrifter, I. Mathematisk-naturv. Klasse, 1895, 

 No. 7. 



