BY C. A. SUSSMILCH AND H. I. JKNSEN. 185 



in grains larger than those of the minerals of the base. The 

 base consists of minute felspar-laths, magnetite-granules, and 

 isotropic dark glass. In addition, this rock contains several 

 large, six-sided, corroded masses of a yellowish colour. They 

 seem to possess a fair cleavage, and faint pleochroism. They 

 appear brownish by reflected light, and have an extremely high 

 double refraction and refractive index. The extinction is 

 shadowy, black crosses forming much the same as where crystals 

 overlap; this feature appears to be due to a twinning lamellation. 

 The mineral is probably a form of rutile. Nepheline may be 

 present in the base, but has not been determined with certainty. 

 Name: Phonolitic Rutile (?) Trachyte. 



C.26. Park (almost black) Trachy-andesite, aphanitic in hand- 

 specimen. Loc: north side of Pinnacle. 



Texture: porphyritic, perpatic with microcrystalline to hemi- 

 hyaline trachytic base. 



Composition : the phenocrysts consist of plagioclase varying 

 from albite to acid andesine. The felspar of the base consists of 

 minute lath-shaped microlites. The pyroxene consists of minute 

 segirine-augite laths, and grains of colourless diopside. Sphene 

 occurs in minute rods, and magnetite in very small rounded 

 grains. Interstitial dark glass is present. In addition, we have, 

 in this rock, fragments of phenocrysts of astrophyllite, with 

 ragged ends and typical micaceous cleavage, and a few pheno- 

 crysts of apatite. This rock appears to be a basic facies of 

 alkaline-trachyte. 



Name : Astrophyllite-bearing Trachy-Andesite. 



No.X.363. Phonolitic Trachyte, Loc: Pinnacle Road. 



Handspecimen : dark, very fine-grained, aphanitic. 



Texture : holocrystalline, very fine-grained, pilotaxitic. 



Composition: felsi)ar, pyroxene, sphene, magnetite, kataphorite, 

 katapleiite and nepheline. The felspar is of two generations: 

 (1) phenocrysts^consisting of anorthoclase and microcline-micro- 

 perthite, almond-shaped in outline and surrounded by a corrosion- 

 rim, and studded with inclusions of diopside and greenish augite. 



