484 ME. J. B.HILL ON PEOGRESSIVE METAMOKPHISM [Aug. 1899^ 



(5699) ISiear Creag Loisgte, Dalmally. — Greenish-grey schistose 

 rock. Eelspar, quartz, carbonates, a nearly colourless micaceou& 

 mineral, chlorite, and iron-ores. 



(5700) Na Cailleachan. — A moderately coarse-grained schist, 

 containing much pale brown mica. Quartz, felspar, carbonates, pale 

 brown mica, and the nearly-colourless (pale greenish) micaceous- 

 mineral mentioned in describing the last specimen. 



In this highly-altered area, between Gleann Strae and Glen Orchy, 

 the limestones are metamorphosed almost beyond recognition. 

 There is one instance of a limestone, | mile south of Beinn Dona- 

 chain, crammed with prisms of actinolite, many of them quite an 

 inch in length. 



Black Slate. — The black slates which occur in association with 

 the limestone do not show in the field the same marked alteration 

 in character as that which has been observed in the Ardrishaig 

 phyllites and the limestone. Corresponding alterations have, never- 

 theless, been induced in them. On the north side of the Pass of 

 Brander, where they occur in association with the limestones and 

 quartz-schists, they are much more micaceous than on the south side 

 of the Pass. A similar change can be distinguished in tracing them 

 from Dalmally to Socach. Near Socach they are also more massive 

 than at Dalmally, as well as darker in hue. In the highly-altered 

 area near Socach and Inverlochy they contain zones of big garnets 

 and actinolites. The garnets are sometimes as big as marbles, and 

 are earlier than the latest foliation which has travelled round them. 

 The beds have also been folded since the introduction of the garnets. 



Grits and Quartzites. — As stated earlier, the black slates pass 

 up into grits and quartzites, with which they are distinctly asso- 

 ciated. In the neighbourhood of Socach is seen the usual succession 

 of the Ardrishaig phyllites giving place to limestones, black slates, and 

 finally grits. The grits, however, have suffered the same extreme 

 metamorphism as that which has afiected the Ardrishaig phyllites, 

 limestones, and black slates. They become quite granulitized and, 

 by recrystallization, pass, in their extreme phase of metamorphism, 

 into gneissose rocks. Among the quartzose rocks both black and 

 white mica have been abundantly developed. But, notwithstanding 

 the amount of granulitization, the coarser grit-bands can still be 

 detected ; although the larger pebbles are flattened, pulled out, and 

 crushed, the alternations in bedding of coarser and finer bands can 

 be seen, and the coarser conglomeratic zones occurring in the less 

 altered beds to the westward are here represented. The black slate- 

 partings are also still recognized, but no longer in the condition of 

 a slate, having been altered into a hard, dark, micaceous rock. 



The pockets of phyllites within the grit, so characteristic of the 

 unaltered beds farther west, are still seen in these highly-altered 

 quartzose beds. Like the slate -partings, however, they have 

 been converted into dull lead-coloured, crystalline, micaceous 

 material. The rocks no longer, in weathering, show the distinctive 



