327 



Examples of this type occur on the slope of Marscow facing the 

 Sligachan Valley, on the west slope of Glamaig, on the hill between 

 Glamaig and Sconcer Inn and on Beinn-na-Cailleach. A coarse- 

 grained granitic rock, composed of felspar and quartz, with a little 

 hornblende and black mica, occurs between Kilbride Manse and Loch 

 Slapin, 



In other localities the felsitic matter predominates ; the crystalline 

 constituents, felspar, quartz and hornblende, occurring as porphyritic 

 elements. The felsite according to ZIRKEL is generally of a grey or 

 greenish grey colour. The quartz of the felsite-porphyries is often 

 well-crystallized and bipyramidal in form. The felspar is much altered 

 and the relative proportion of orthoclase and plagioclase is not 

 constant. In a rock from the north slope of Glamaig plagioclase 

 predominates. Liquid inclusions occur in the quartz and cubes (? salt) 

 are sometimes present in them. Hornblende microlites are frequently 

 scattered through the felsitic matter. The holo-crystalline quartz- 

 syenites and the felsite-porphyries are connected by transitional forms. 

 The felsite of the rock from the north slope of Glamaig is resolved by 

 the microscope into micro-pegmatite. Rocks similar to those of Skye 

 occur also in the Island of Mull. So far we have been quoting 

 Professor ZIRKEL. The author is indebted to Mr. WATTS for 

 a specimen from the east side of Glen Sligachan, Skye, and for 

 two specimens from the base of Craig Craggen in the Isle of Mull. 

 The specimen from Glen Sligachan is a hornblende-granitite. The 

 hornblende (green) is abundant ; black mica is scarce. Apatite, iron- 

 ores and sphene also occur. This rock has affinities with the sphene- 

 bearing hornblende-granitites of Fort William and Dalbeattie. The 

 specimens from Craig Craggen are most beautiful examples of augite- 

 bearing granophyres (see Fig. 1, Plate XXXIIL). The one is grey, the other 

 pinkish grey. Both are finely crystalline and granular in appearance. 

 Under the microscope they are seen to be composed principally of quartz 

 and felspar. The ferro-magnesian constituent is a green augite. There 

 is also a little magnetite. The augite and magnetite form an extremely 

 small portion of the entire mass. The felspar is almost entirely 

 orthoclase. It often occurs in Carlsbad twins, both halves of which 

 extinguish simultaneously when the twin-line coincides with one of the 

 cross wires. The orthoclase-individuals lie in a matrix of micro- pegmatite, 

 and the orthoclase of the micro-pegmatite which immediately surrounds 

 one of the larger individuals generally extinguishes simultaneously with 

 that individual. This feature has already been referred to in describing 

 the so-called syenite of Ennerdale in the Lake District. The augite 

 occurs in irregular grains. It is richly coloured even in thin section. 

 That it is augite and not hornblende is proved by its cleavage, by its 

 extinction in the zone of the vertical axis (maximum observed 42) 

 and by the absence of pleochroism. These rocks have the closest 

 affinities with the rock of Barneveve in the Carlingford District (Ireland). 

 They also have affinities with the " micro-granulite " ejected from the 



