Vol. 56.] AND OTHER IGNEOUS ROCKS IN ARGYLLSHIRE. 551 



ph}Tes ; and the decided syenitic tendency of the central portion of 

 this sill is doubly interesting, in connexion with the relationships 

 which we have shown to exist between such augite-diorites and 

 kentallenite. 



V. General Considerations. 



In the foregoing pages we have described the principal varieties 

 of kentallenite, hitherto known as occurring in Argyllshire ; we 

 have endeavoured to indicate their penological affinities, and have 

 pointed out their relationships to the granites, diorites, and lampro- 

 phyres of the areas in which they occur. It now remains briefly to 

 refer to a few considerations of a more general nature. 



Prom a study of the intrusive rocks of the Ben-Bhuidhe area, 

 we cannot avoid the conclusion that the various intrusive 

 types, from kentallenite to granite, constitute a closely- 

 related assemblage, which have all been derived from 

 an original common magma. The evidence which we have 

 brought forward as to the inter-relationships of the different 

 rocks, is strongly confirmed in the other areas where kentallenite 

 occurs. And these areas have, petrographically, so many features in 

 common with that of Ben Bhuidhe, that we are led to infer that 

 what has taken place in the one area has also taken place in the 

 other. Prom a petrographical standpoint, we may subdivide the 

 general district, — as we have already done for the sake of con- 

 venience in description, — into secondary areas of intrusion, or 

 eruptive foci, each characterized by important masses of acid 

 material, about which secondary intrusions of more basic character 

 are apparently arranged as about a nucleus. In each area, differenti- 

 ation has evidently followed along parallel lines. The physical 

 conditions have been approximately similar, and similar rock-types 

 and similar phenomena of intrusion have been the result. Prom 

 this, one is naturally led to suppose that the original magmas of 

 each eruptive centre resembled one another more or less closely in 

 chemical composition. Is it not then extremely probable, considering 

 the comparative proximity of the different centres, that the sources 

 of supply for each proceeded from one parent-magma ? We must 

 suppose that the reservoir for each centre owed its origin either to a 

 more deep-seated general magma, or to the splitting up by some 

 means, such as crust-movement, of one large magma into secondary 

 reservoirs, while it was still more or less homogeneous. 



Since the phenomena of intrusion are more or less similar in each 

 centre, we may confine ourselves to the Ben-Bhuidhe area in dealing 

 shortly with the remaining points which call for attention. Owing 

 to the close relations existing among the various rock-types which 

 constitute the Ben-Bhuidhe complex, it is evident that they belong to 

 the same general geological period, but at the same time it would be of 

 interest if some definite sequence among the different intrusions could 

 be established. The evidence, such as it is, appears to show that the 

 kentallenites represent the earliest intrusions of this 

 area. The mass exposed in the An-Sithein burn is seen to be cut by 



