Vol. 56.] AND OTHER IGNEOUS ROCKS IN ARGYLLSHIRE. 541 



III. The Relation between the Kentallenites and the Granites 

 and Diorites. (See Map, p. 542.) 



As we have already pointed out, kentallenite invariably occurs in 

 areas which have been invaded by various intrusive rocks such as 

 granite, diorite, iamprophyre, etc. And, moreover, one may see 

 at a glance that that portion of Argyllshire over which kentallen- 

 ites are distributed, naturally divides itself into four intrusive areas, 

 at no great distance one from the other. Thus we have (1) the 

 Ballachulish area, characterized by the Ballachulish granite, 

 various diorites and allied intrusions, and the basic rock of Kentallen ; 

 (2) the Ben-Gruachan area, characterized by the enormous 

 granite-masses of Ben Cruachan and Glen Etive, augite-diorites, and 

 numerous sills and dykes of porphyrite, to which we may add the 

 kentallenite-intrusion of Glen Orchy ; (3) the very much smaller 

 area of Loch Avich, characterized by several small granitic 

 intrusions, recently mapped by our colleague Mr. R. G. Symes, in 

 the neighbourhood of Kilmelfort, and the kentallenite exposed to 

 the west of Loch Avich; and lastly (4) the Ben-Bhuidhe area, 

 characterized by intrusions of granite, tonalite, augite-diorite, 

 numerous lamprophyres, and the olivine-augite-orthoclase rocks of 

 the Brannie and An-Sithein burns. 



It would be beyond the scope of this paper to enlarge upon the 

 various features which these four areas possess in common. It will 

 be sufficient for our purpose to emphasize the fact, already indicated 

 above, that in each area there is on the whole a generally similar 

 assemblage of intrusive rocks, whose basic representative is in each 

 case almost identical. 



The inference seems obvious, therefore, that the development of 

 the basic type took place under conditions almost identical in 

 each area. Further, in each case, the various intrusive types 

 appear to be so closely related one to the other, that we believe that 

 they represent the products, during different phases of activity, of a 

 common parent-magma. But until the ground had been surveyed 

 in detail, the relationship of the kentallenites to the other intrusions 

 did not seem particularly clear. We are now, however, able to 

 present evidence, which shows that this particular group bears as 

 close a relation to some of the diorites, as the diorites themselves 

 bear to the granites. The greater part of our material has been 

 derived from field-observations in the Ben-Bhuidhe area, supple- 

 mented by the microscopical investigation of numerous sections 

 prepared for the Geological-Survey collection from our specimens. 



It is in the Ben-Bhuidhe complex of igneous rocks that the 

 relationships of the kentallenites are perhaps most clearly shown. 

 We shall therefore, in what follows, deal more particularly with 

 that area. We believe, at the same time, that similar relationships 

 are also indicated in the other Argyllshire areas where our basic 

 type occurs, and that, although the evidence which they furnish 

 may not be so complete, they will abundantly confirm the con- 

 clusions that we have drawn from a comparative study of the Ben- 

 Bhuidhe rocks. 



Q. J. G. S. No. 223. 2 o 



