386 ME. H. H. THOMAS ANB rROr. 0. T. JOJfES ox THE [Sept. I912, 



A breccia from Hayscastle (E 7770) belonging to this series has 

 a beautiful purple colour and, under the microscope, shows itself to 

 be composed of fragments of devitrified quartz-keratophyres. The 

 felspar-phenocrysts are, as usual, all albite, and in the ground-mass 

 it is possible to detect traces of the original handing of the rock 

 and to make out fluxion and even perlitic structures. 



Specimens taken from the Rhindaston mass, on the eastern side 



Fig. 1. — Quartz-L-eratophyres from the Rhindaston and 

 Gignog Group. 



A. B. 



E 8992 E 7238 



A. From the western side of Brandy Brook, east of Asheston, showing cor- 



roded phenocrjsts of quartz and turbid crystals of albite in a felsitic 

 ground-mass with fluxion-structure (magnified 25 diameters). 



B. From crags on the eastern side of Brandy Brook, south of Grignog, showing 



phenocrysts of quartz and albite in a fine-grained, devitrified and silicified, 

 felsitic ground-mass (magnified 25 diameters). 



of Brandy Brook, show the rocks to be lavas and associated tuffs 

 (E 7230, 7237-7241). The lavas contain a few small corroded 

 quartz-phenocrysts, but have a preponderance of albite-felspar 

 (E 7238, fig. 1 B). The ground-mass is composed of microcrys- 

 talline quartz and albite, but it contains locally a considerable 

 quantity of epidote, the presence of which suggests the possibility 

 of the felspars being at one time richer in lime than they are at 

 present. This is the only indication, however, of albitization 

 observable in these rocks, and it is probably not wholly trustworthy. 



