486 ME. J. B. HILL ON PKOGEESSIVE METAMOEPHISM [Aug. 1899^ 



one recedes from the granite the large crystals are no longer 

 observed. The felspar occurs also in veins and strings along joint- 

 planes, or even along foliation-planes, and in these latter the felspar 

 increases in amount as a joint-plane is approached. Usually, how- 

 ever, when at some distance from the granite the felspar occurs as 

 small isolated red grains irregularly scattered through the rock. 

 "While there can be no doubt that in the neighbourhood of the granite- 

 margins the felspathic material has been introduced into the schist, 

 it cannot be demonstrated that this is the case when we are dealing 

 with the isolated felspathic grains at some distance from it, as the 

 schists themselves were originally rich enough in felspar to have 

 supplied the necessary material. 



It may be added that these secondary felspars are similar to 

 those contained in the granites, some, for example, are orthoclase, 

 others are alkaline felspar enclosing oligoclase, and there are also 

 traces of microperthite. All these characters have been detected in 

 the felspars of the granite. 



Epidiorites, etc. — The epidiorites and hornblende-schists have 

 undergone great alteration in this highly-metamorphosed area 

 between Gleann Strae and Glen Orchy. They have been considerably 

 granulitized and partially recrystallized. The hornblende is usually 

 darker, and black actinolite has often been developed. In this 

 particular district of Gleann Strae and Glen Orchy the chlorite that 

 occurs in the unaltered area to the south and south-west has been 

 converted into hornblende. The porphyritic crystals of felspar 

 which have been described as occurring with clear crystalline out- 

 lines in the chlorite-schists and chloritic hornblende-schists to the 

 west have been considerably granulitized, and are here represented 

 only by irregular blotches ; their character, however, can clearly 

 be recognized. Biotite and garnets are common as accessory 

 minerals. A specimen was selected from a hornblende-schist in 

 the highly-metamorposed area and reported on by Mr. Teall a& 

 follows : — (5689) Dark greenish crystalline schist. Hornblende, 

 biotite, quartz, and felspar ; structure granulitic. Coarser bands 

 or veins of quartz and idiomorphic felspar occur in the granulitic 

 schist. Hornblende-biotite-schist. 



In the neighbourhood of Socach, where the epidiorites occur, 

 crystals of secondary white mica have been observed in them. 

 Epidote is also a common accessory mineral in this neighbourhood. 



A remarkable type of epidiorite that occurs about 2 miles south- 

 west of Dalmally may be conveniently described here. It occupies 

 an area considerably over a square mile in extent, just where a rapid 

 change of metamorphism is first beginning to be observed. While 

 the peculiarities of the rock cannot be altogether claimed as a 

 product of metamorphism, its occurrence in the critical zone of 

 rapidly-changing conditions and within a mile of the Cruachan granite 

 is suggestive. The eastern part of this mass is a coarse hornblende- 

 felspar rock, not very schistose, in which the hornblendes are often 

 of considerable size ; but the rock frequently becomes fine-grained.. 



