556 MESSES. HILL & KYNAST0N ON KENTALLENITE [Aug. I9OO, 



that these latter may be connected by transitional types with acid 

 biotite-granites. The augite-diorites, allied to kentallenite, occur, 

 not only as separate intrusions, but also as the marginal modification 

 of a granite-intrusion. Similar relationships are found to hold good 

 in the other Argyllshire areas where kentallenite is found, namely 

 that of Ben Cruachan, that of Loch Avich and Kilmelfort, and that of 

 Ballachulish. Moreover, kentallenite proves to be not only thus 

 connected with the intrusions of diorite and granite, but also to have 

 close relationships to the numerous lamprophyre-intrusions which are 

 a characteristic feature of that portion of the Ben-Bhuidhe area which 

 has been invaded by the more basic plutonic masses. Among these 

 lamprophyres we have described certain basic types, rich in pyroxene, 

 both from the Ben-Bhuidhe and Ben-Cruachan areas, and have 

 indicated the relationships between these and the augite-diorites, 

 allied to kentallenite. The basic lamprophyres again are shown to 

 be connected with the camptonites and hornblende-porphyrites by 

 a series of intermediate varieties. We thus may conclude that the 

 Ben-Bhuidhe complex of intrusive rocks constitutes a closely related 

 and associated assemblage, ranging, in the plutonic phase, from granite 

 to kentallenite, and, in the dyke- or sill-phase, from orthoclase- 

 porphyry and porphyrite to augite-lamprophyre ; and further, that 

 this assemblage has been derived by a process of differentiation from 

 one parent-magma. The order of intrusion in this area 

 has been in the main in the order of increasing 

 acidity. 



Not only have we a series of rocks consisting of separate intrusions 

 of varied rock-types owning a common origin, but also a facies- 

 suit, constituting one of these intrusions, and showing a progressive 

 increase in basicity from centre to margin. In the one case 

 (facies-suit) differentiation has taken place subsequently to in- 

 trusion, and in the former case under more deep-seated conditions, 

 previously to intrusion. In each case we suppose that there has 

 been a concentration of the more basic oxides in the more marginal, 

 and therefore cooler portions of the magma, and that this process 

 has resulted finally, in the case of our series of separate intrusions, in 

 the outer portion of the magma becoming richer in basic oxides, and 

 so capable of erupting a variety of basic rocks into the more marginal 

 portion of the area, while the central part has been invaded by more 

 acid rocks. In the facies-suit differentiation took place in situ, 

 and was followed by consolidation of the mass, so as to produce an 

 intrusion with an acid core passing gradually into a basic marginal 

 portion. The magma, from which the various rock-types were 

 derived, was probably originally of more or less intermediate com- 

 position, differentiation in which probably resulted in the production 

 of ' complementary ' rocks, constituting the extremes of the rock 

 series. Furthermore, the close parallelism between the intrusive 

 phenomena of the other Argyllshire eruptive areas and those of Ben 

 Bhuidhe, renders it extremely probable that in each area a similar 

 type of differentiation took place along parallel lines ; and from the 

 fact that in each case more or less similar rock-types have been 



