442 Major G. W. Williams— 



approximately equal amount. The accessories are abundant apatite, 

 some fairly large zircons, magnetite, and allanite. 



101. ^jirine-riebeckite-porphyry. — A porphyritic rock with 

 phenocrysts of white felspar in a bluish-grey groundmass. The 

 felspars are rather lath-shaped and up to 8 mm. in length. They 

 consist of orthoclase and occasionally enclose a little quartz. The 

 groundmass is a rather fine mosaic of orthoclase felspar, segirine, 

 and riebeckite, with a little quartz. 



102. RhyoUte. — This rock possesses conspicuous flow-structures, 

 shown by wavy bands of dark red and dark blue colours. It is much 

 stained by iron oxide and other decomposition products, but under 

 the microscope shows well-marked micropoecilitic structure, with a 

 tendency to aggregation in spherulites. It is probably a devi trifled 

 glassy lava of acid composition. 



103. Microclme-granite. — A coarse-textured granitic rock, con- 

 siderably crushed and granulitized. It consists almost entirely of 

 quartz and microcline felspar, with a very small quantity of 

 muscovite. There is a slight tendency to micrographic structure. 

 The rock is evidently of very acid composition, but it is a good deal 

 decomposed, with much infiltration of secondary products along 

 cracks and the boundaries of the minerals. 



105. Rieheckite-hiotite-granite. — A granitic rock of coarse texture, 

 composed of quartz, microcline, subordinate plagioclase considerably 

 decomposed, and riebeckite, with a little biotite. The accessories are 

 iron oxide, apatite, and zircon. 



106. Granite. — This specimen consists of quartz, decomposed 

 orthoclase with some plagioclase near oligoclase, and patches of a 

 green chloritic mineral, which may represent biotite. The rock has 

 been much crushed, as is shown by the bending of cleavages and the 

 twin-lamellse of the plagioclase. 



107. Gabbro. — A remarkably fresh rock, consisting of plagioclase 

 felspar, diallage, hornblende, and a little biotite. The felspar has 

 a refractive index higher than that of Canada balsam, and shows 

 extinction angles up to 30 degrees. It is therefore of a basic character 

 near labradorite. The diallage is very pale brown, with the 

 characteristic purplish inclusions. There is also some colourless 

 augite. The brown hornblende is often seen as a sort of graphic 

 intergrowth with the pyroxene, all the enclosed patches commonly 

 showing the same orientation. There is a little bright chestnut- 

 brown biotite (lepidomelane). The only accessory mineral is a very 

 little magnetite and no nepheline or analcime could be detected. 

 The extraordinary freshness of this rock suggests that it is of much 

 later date than any of the other specimens. 



108 and 110. Biotite-granite. — Both these specimens, which are 

 almost identical, are granulitized gneissose granites, composed of 

 quartz, often in rounded blebs in the felspar, large microclines, and 

 a little plagioclase. There are here and there small patches of 

 micropegmatite. The coloured constituent is olive-brown biotite. 



