BY H. C. RICHARDS. 161 



the relative amount and size of the inclusions, but in the 

 andesites from near Point Danger, in some cases, the 

 phenocrysts seem almost wholly composed of very fine 

 opaque inclusions. 



The groundmass is in all cases hyalopilitic, and in some 

 of the lavas it shows a definite fluxion structure. The 

 crystals in the groundmass are plagioclase, augite, magne- 

 tite and ilmenite. The plagioclase usually shows simple 

 twinning only, though in some, lamellar twinning is present. 

 It is slightly more acid in the groundmass than in the 

 phenocrysts, and ranges from medium andesine. Ab,j5An35, 

 to basic andesine, Abj^An^^. In size the laths range from 

 •05 mm. to -15 mm. in length. Augite occurs in two 

 generations in several rocks, but it is usually in very 

 small grains in the groundmass. 



The iron ores may occur as small granules or rod-like 

 fragments -3 mm. long. The amount of glass in the ground- 

 mass varies greatly but it never exceeds the crystals in 

 amount. It is usually a light brown in colour and crowded 

 with triehites &c. Ophitic structure is not seen in any 

 of the sections. 



A few of the more representative rocks are here 

 ■described. 



Specimen 136. — Locality: Lookout, Springbrook 

 Plateau, portion 84, parish of Xuminbah. This andesite 

 occurs as a flow and forms the summit of MacPherson's 

 Eauge at the southern termination of the Springbrook 

 Plateau. The rock is perpatic and has phenocrysts of 

 medium andesine ranging up to 2 mm. long, and violet- 

 coloured sub-idiomorphic augite crystals up to -75 mm. in 

 diameter, set in a hyalopilitic groundmass showing good 

 fluxion structure. 



The plagioclase in the groundmass ranges from -05 

 mm. to -3 mm. in length, and the augite is present in very 

 fine granules. Very small granules occur abundantly through 

 the section. The plagioclase phenocrysts show zoning in 

 some cases, and twinning of the augite phenocrysts is seen 

 occasionally. The specific gravity is 2-79. Name: Ande- 

 site. 



