\ ol. 56.] AND OTHER IGNEOUS ROCKS IN ARGYLLSHIRE. 557 



produced, we may conclude that the underlying magmas resembled 

 one another more or less closely in composition. These somewhat 

 similar sources of supply doubtless represent local magmas, derived 

 from a more general magma-basin. 



In conclusion, we would express our cordial thanks to Mr. J. J. 

 H. Teall, F.R.S., for valuable hints and suggestions in the micro- 

 scopical examination of many of our rock-types. 



EXPLANATION OF PLATES XXIX-XXXI. 



Plate XXIX. 



Fig. 1. Kentallenite froin Kentallen Quarry, near Ballachulish (Argyll): 

 type-rock. (See p. 534.) Of. Teall, 'Brit. Petrogr.' pi. xvi, fig. 1. 

 The slide shows olivine-grains, with anastomosing cracks filled with 

 magnetite; idiomorphic augite; ragged plates of biotite, which are 

 moulded on the olivine, augite, and plagioclase. The clear portion 

 consists of more or less idiomorphic plagioclase and interstitial ortho- 

 clase in approximately equal proportion. X 14. 

 2. Kentallenite from Glen Orchy (Argyll), from a portion of the mass rich 

 in basic minerals. The slide shows much olivine, marked by a network 

 of cracks, and augite in smaller quantity. Biotite and felspar appear 

 to play the part of groundmass to the olivine and augite. There is a 

 decidedly smaller proportion of orthoclase in this rock than in the 

 Kentallen type. X 14. (See p. 534.) 



Plate XXX. 



Fig. 1. Phase of the Glen-Orchy mass, with structure resembling the por- 

 phyritic. Idiomorphic augite and more or less idiomorphic olivine 

 are conspicuous in a groundmass of small biotite-flakes and felspar. 

 Neighbouring flakes are often seen to be in optical continuity, and 

 to be moulded upon the plagioclase. Xl3^. (See p. 534.) 

 2. Kentallenite from Allt-an-Sithein, Ben-Bhuidhe area. This shows 

 more orthoclase and decidedly less olivine than the three preceding 

 figures. The idiomorphism of the augite is seen to be far less perfect 

 than in the more basic types from Kentallen, etc. There is not so 

 much biotite as in the Brannie-Burn rock. The orthoclase occurs in 

 micropcecilitic patches, in which the plagioclase-laths are embedded 

 without orientation. This rock contains hypersthene, in more or les& 

 corroded grains, in addition to the augite. x 13^. (See p. 535.) 



Plate XXXI. 



Fig. 1. Marginal portion of intrusive mass on Beinn Chas, Ben-Bhuidhe area. 

 X 13^. (See p. 544.) Augite is abundant showing more or less idio- 

 morphism, and often a narrow alteration-border of green hornblende. 

 Small biotite-flakes and more or less idiomorphic plagioclase may also 

 be seen. A very small proportion of alkali-felspar may possibly be 

 present. The rock resembles some of the more basic lamprophyres 

 of the district, as well as the augite-diorite, occurring north-west of" 

 Clachan Hill, related to kentallenite. 

 2. Quartz-diorite of the tonalite-type, part of the same intrusion as the 

 preceding, but from a more central portion. X 13f . (See p. 545. ) 

 The slide shows green hornblende, biotite, more or less idiomorphic 

 plagioclase (turbid from alteration), orthoclase, and interstitial quartz. 

 This type passes in the central portion of the mass, by the loss 

 of hornblende and the increase in proportion of felspar and quartz, 

 into a biotite-granite (of the Ben-Bhuidhe type). 



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



