CHAEACTEES OF A SEETES OF SCOTCH EOCKS. 165 



slightly porphyriti-c, of series II. ; almost identical with rocks I have 

 described from Ben Eyn. 



21 (towards upper end of Attadale Valley, north side). A finer, 

 less micaceous gneiss ; but microscopically it has only varietal diffe- 

 rences from ]STo. 20, so II. 



22 (Ben Nan Tom, head of Loch Shiel). A heavy black horn- 

 blende rock, with a parallel structure resembling one extremely 

 metamorphosed. Under the microscope it exhibits numerous dark- 

 green hornblende crystals, well cleaved and sometimes affording 

 definite external faces ; with these are brown mica, sphene, and 

 grains of quartz, and of a plagioolase felspar, which has a rather 

 large extinction- angle. The structure of this rock reminds me 

 strongly (except that garnets are absent) of one described from Ben 

 Eyn which was certainly intrusive ; and I cannot help suspecting 

 it, notwithstanding its gneissic aspect, to be really a diorite. 



23 (Ben Nan Tom). A handsome, rather coarse, pinkish and dull 

 greenish gneiss. Consists of quartz, felspar and dark mica, with a 

 little epidote, apatite, and garnet. The mica is partly replaced by a 

 dull-green chloritic mineral; and between its cleavage-planes are 

 occasional plates of a clear felspathic mineral. The curious ver- 

 micular or micrographic structure often noted in highly altered 

 gneisses is present in parts of the slide. I should unhesitatingly 

 class this with III. 



24 (Druiin na Saille, head of Loch Eil). A fine-grained gneiss of 

 the same type as 20, and, like it, a good example of II. ; contains 

 sphene, epidote (?), and, I think, a little apatite. 



25 (Kilmallie, Loch Eil). A brownish silvery mica-schist. Ex- 

 amined microscopically, it shows so much felspar (rather decomposed) 

 as to make the term gneiss more correct ; both brown and white 

 mica are present ; the former a little altered. The micas are some- 

 times interlaminated, and the brown exhibits the inclusions noted in 

 No. 23 ; some apatite is present. Decidedly II. 



26 (shore of Loch Eil, west of Kilmallie). A rather compact dull 

 green rock. Consists microscopically of a plagioclastic felspar, with 

 large extinction-angles, often much altered, and rather pale hornblende. 

 There has been a little brown mica ; and there is a fair quantity of 

 sphene. I have no doubt the rock is an igneous one, and, as I regard 

 the hornblende as a secondary product, name it a hornblende- 

 diabase. 



27 (Banavie). A reddish felspathic granitoid rock. Microscopi- 

 cally consists of quartz, felspar (orthoclase, microcline, and a plagio- 

 clase), with a little rather decomposed brown mica. The structure 

 is somewhat exceptional ; and I have had doubts whether this may not 

 be a granitoid gneiss, but on a single slide, and without field- 

 knowledge, will not venture to express a decided opinion. 



28 (road to Duncraig, from Strome). A flaggy hard mudstone, 

 looking little, if at all, metamorphosed. Under the microscope 

 clastic quartz, felspar, and mica are very distinct ; but there is a 

 considerable quantity of very minute " sericite," which gives to the 

 rock a microscopic foliation ; this implies a certain amount of meter 



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