AMPHIBOLITES AND RELATED ROCKS-STILLWELL. 277 



very fine; and there are thin lenticles of felspar arising from it. Some of this felspar 

 is imr\viiim><l ; l>ut some lamellse show an extinction angle of 33 indicating a labradorite. 

 There are scattered crystals of ilmenite and apatite. This type of schist is distinct 

 from the other hornblende-plagioclase-gneisses, and the quartzitic nature of the ground 

 nniss suggests its derivation from a sedimentary rock. 



Specimen No. 924 is another type of hornblende-plagioclase-schist, which is 

 also more basic than typical members of this group. The base of the rock consists 

 of densely-packed acicular needles of hornblende, with grains of epidote set in a 

 colourless base of clear felspar and quartz. The hornblende needles have a pale green 

 colour and an extinction of 20. The rock also possesses relic phenocrysts of quartz 

 and felspar, and in this way resembles a " porphyroide." Some of the felspars have 

 an extinction of 27 J indicating labradorite and some are studded with numerous small 

 crystals of epidote. These relic crystals indicate that the rock has developed from a 

 porphyritic igneous rock, probably a felspar porphyrite. The abundance of epidote 

 is a feature belonging to the Epi division of this group. 



EPI DIVISION. 



This division includes the group of the epidote felspar gneisses. Some of these 

 appear to grade into the Epi division of Group I, the Alkali-Felspar Gneisses, while 

 others grade toward the Epi divisions of Groups IV, V, and IX, the Amphibolites and 

 Edogitea, the Magnesium Silicate Gneisses and the Lime Silicate Gneisses. 



Typical of these epidote gneisses is specimen No. 257, in which the colour of 

 the specimen is dominated by the green epidote. It is a green schistose rock with a 

 banded structure and a much finer grain than preceding types. It possesses a distinct 

 crystallisation-schistosity, and some of the bands possess a darker green colour than 

 the average, on account of the association of chlorite and hornblende with the epidote. 

 In section, the light coloured bands consist of granoblastic masses of clear felspar, with 

 scattered flakes of pale chlorite and epidote. The felspar consists of microcline felspar 

 and albite. In some bands epidote (with a little zoisite) is the most important mineral; 

 while in others a pale green hornblende is as abundant as the epidote. The hornblende 

 represents the residual mineral, which has survived the general alteration into epidote 

 and chlorite. Its colour is bleached prior to this alteration; and areas of residual 

 green mineral ;ire observed, surrounded by colourless hornblende partly converted 

 into chlorite. Sphene and apatite are present, and a few epidote grains possess a 

 reddish-brown nucleus of allanite. 



In ;i similar specimen, No. 157, some of the bands of pink felspar are broader, 

 being as much as 5mm. wide, while others are darker and possess a larger percentage 

 of hornblende. In this case, and in No. .VJ-J. quartz is present. In No. 522, the 

 pale green hornblende changes into a colourless horn Monde prior to its alteration to 

 epidote and chlorite. Many of the epidote grains contain a reddish-brown nucleus 

 which is probably allanite. 



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