Vol. 56.] AND OTHER IGNEOUS ROCKS IN ARGYLLSHIRE. 547 



we have already drawn attention to the occurrence of kentallenite in 

 the same area. The granitic intrusions consist of biotite- granite, 

 quartz-diorite, and augite-granite. One exposure of augite- 

 granite is not more than 2| miles from the Loch-Avich kentallenite. 

 It occurs on the northern shore of Loch-a-Chaoruinn, about 1| miles 

 west-north-west of the head of Loch Avich. The other intrusions 

 are found farther westward, east and south-east of Kilmelfort. 



The augite-granite consists of an almost colourless augite, pale 

 green hornblende, biotite, plagioclase, orthoclase, interstitial quartz, 

 and accessory magnetite [8566 & 8575]. The plagioclase is largely 

 in excess of the orthoclase. In the quartz-diorite [8571] we find a 

 brown idiomorphic hornblende, resembling the variety characteristic 

 of camptonite. 



Here again we have a similar assemblage of intrusive rocks, though 

 the transitional varieties are not so numerous. It is interesting to 

 note, however, that here also the association of a pale augite and 

 interstitial orthoclase characterizes other and more acid intrusions 

 than those of the basic type of Loch Avich, thus serving to connect 

 the basic type with the diorites and granites. 



Passing now to the Ballachulish area, we find west and 

 south-west of the granite-mass of Ballachulish, besides the intrusions 

 of kentallenite already described (pp. 533-34), three intrusions of 

 augite- diorite, which have been mapped by Mr. J. Grant- Wilson. 

 They occur, as may be seen by a glance at the sketch-map (p. 542), 

 at no great distance from the granite- margin : — at Ardshiel Hill, 

 less than a mile south-west of Kentallen ; at Budha Mor ; and on 

 Eilean Bain ago wan. The rocks are referred to as follows in the 

 Annual Eeport of the Geological Survey for 1896, pp. 21 & 22 : — 



'The rock of Eilean Balnagowan is a diorite with a somewhat exceptional 

 amount of orthoclase, and possessing, therefore, affinities with the syenites ; that 

 of Rudha Mor is a quartz-augite-diorite ; and that of Ardshiel Hill an augite- 

 diorite, with a small amount of quartz. All these rocks contain a small quantity 

 of interstitial quartz and alkali-felspar; a fact which shows that they are 

 merely basic modifications of the magma which has produced the larger granite- 

 masses of Ballachulish and Ben Nevis.' 



We have examined these rocks under the microscope, and 

 were at once struck with the resemblance between them and the 

 augite-diorites, described on p. 546, from near Glen Strae in the Ben- 

 Cruachan area. The granite-mass of Ballachulish, moreover, closely 

 resembles that of Ben Cruachan, and varies from diorite to horn- 

 blende-granite, becoming on the whole more acid as we approach 

 the inner portion of the mass. Here, then, is a marked repetition of 

 similar phenomena. We cannot dissociate the augite-diorites from 

 the granite, while on the other hand there is strong evidence of the 

 former being related to the more basic kentallenites ; and we cannot 

 but conclude that the evidence, which is so well brought out by a 

 comparative study of the Ben-Bhuidhe rocks, is strongly confirmed 

 in the other granitic centres of Ben Cruachan, Loch Avich, and 

 Ballachulish. 



