BY C. A. SUSSMILCH AND H. I. JENSEN. 179 



kilitic aggregates of cossyrite and arfvedsonite, acicular gegirines, 

 segirine-augite grains, corroded magnetite, red iron-ores, and a 

 few specks of sphene(?j. 



Name : Porphyritic Soda-Trachyte. 



C.21. A somewhat decomposed, otherwise normal, porphyritic, 

 soda-trachyte, containing interstitially some grains of free quartz. 

 Ferrite occurs as an abundant alteration-product of aegirine- 

 augite and soda-amphibole. Loc: near Bald Knob. 



No.X.eSS. Tracliyte-Porphyry. Loc: The Pinnacle. 



Handspecimen : coarsely porphyritic, iron-stained, light-coloured 

 rock. 



Texture : holocrystalline ; porphyritic, dosemic ; with fine- 

 grained trachytic base. 



Composition : main constituent felspar. In addition we have 

 2 % to 3 % of light green augite. The felspar phenocrj^sts are 

 hypidiomorphic, corroded, and exhibit a shadowy extinction 

 clearly due to ultramicroscopic twinning; frequently this is so 

 marked as to give the appearance of the ^i7^e?^-structure of micro- 

 cline. Carlsbad twinning is well-marked. The inclusions consist 

 of ?egirine-augite and glass. Clearly these phenocr3^sts consist 

 of microcline microperthite and cryptoperthite. The felspar of 

 the base consists of the usual microlites of tabular and nephi- 

 linitoid habit, showing CarLsbad twinning; they consist of soda- 

 sanidine, and give the base an orthophyric-trachytic fabric. The 

 pyroxene is a colourless to light green variety of eegirine-augite, 

 with an extinction angle of 33°. 



This rock appears, from field-occurrence, to be the remnant of 

 a sill. Its micro-structure is indicative of hypabyssal origin; for 

 this reason we call it Porphj^ritic ^girine-Augite Solvsbergite. 



No.X.648. Trachyte-Porphyry. Loc: The Pinnacle. 



Handspecimen : Miarolitic, coarsely porphyritic rock stained 

 with iron-ores. 



Texture : holocrystalline, porphyritic, serial, dosemic; base 

 hypidiomorphic-granular, near orthophyric in fabric. 



