Vol. 56.] KENIALLENITE AND OTHER ARGYLLSHIRE ROCKS. 543 



The Ben-Bhuidhe area covers a mountainous tract to the 

 west of Glen Fyne, and between that glen and Glen Shira. In 

 its more central portion Ben Bhuidhe forms a well-defined ridge, 

 rising to slightly over 3000 feet above sea-level. On this ridge 

 occur two somewhat irregularly-shaped masses of granite, of a 

 medium-grained and rather acid type, resembling some of the finer- 

 grained portions of the Glen-Fyne intrusion. In dealing with 

 these granites it must be borne in mind that they are undoubtedly 

 related to the far larger intrusive mass of Glen Fyne, and doubtless 

 constitute subordinate modifications of the same magma. The intru- 

 sions on Ben Bhuidhe are not more ' than 2 miles from the nearest 

 exposure of the Glen-Fyne mass, and there are close petrological 

 relationships between them. 



These granites represent the more acid intrusions of the Ben- 

 Bhuidhe complex. Between them and our most basic type, repre- 

 sented by the kentallenites of the Brannie and An-Sithein burns, 

 come several intrusions of more intermediate type, such as augite- 

 diorite andtonalite, which we regard as constituting connecting- 

 links between the two extremes. In addition to these we find 

 numerous lamprophy res of varying type, especially well-developed 

 in Glen Shira, representing the more basic end of the series in terms 

 of dykes and sills ; while the more acid end is represented by por- 

 phyrites and orthoclase-porphyries, more especially developed 

 in and about Glen Fyne„ We have, then, in the Ben-Bhuidhe area 

 an assemblage of intrusive rocks — on the one hand belonging rather 

 to the boss-like or laccolitic type of intrusion, and ranging from 

 granite to olivine-augite rocks containing orthoclase ; and on the 

 other hand belonging to the dyke- or sill-phase, and varying from 

 orthoclase-porphyries to basic lamprophyres. 



A mass of diorite of evidently basic affinities is well exposed 

 \ mile north-west of Clachan Hill, and about f mile from the 

 olivine-augite-rock of Brannie Burn. It forms an elongated sill- 

 like mass, about \ mile long and \ mile broad, on the steep slope 

 between the Clachan-Hill ridge and Brannie Burn ; and from 

 its dark aspect and rugged mode of weathering, the rock at first 

 sight recalls kentallenite. A closer inspection, however, at once 

 shows that we are dealing with a less basic type. The rock is 

 almost black in hand- specimens, and augite, biotite, and felspar may 

 be seen with a lens. An occasional, though rare, grain of what is 

 apparently olivine may also be detected. Under the microscope 

 [8461], the rock is seen to be composed of nearly colourless 

 augite, biotite, green hornblende, plagioclase, and a little interstitial 

 quartz. A very small amount of orthoclase-felspar may also be 

 detected, occurring interstitially. The rock is somewhat altered, 

 and carbonates are present. Olivine is occasionally seen in the 

 form of inclusions in the augite. 



Comparing this rock with our more basic type of the Brannie and 

 An-Sithein burns, we find that olivine is decidedly rare. The rock, 

 however, is rich in augite, and the mineral is of the same variety as 

 that characteristic of the An-Sithein and Brannie rocks. The biotite 



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