HORN EXPEDITION PETROLOGY. 95 



Fi<?. 2. — Fine-grained Dokrife. No. 121 x '..'. Drawn in ordinary \vj}\i. 

 Augito, plagioclaso, and inagnetitp readily distinmiishahlo. Tho moro 

 indefinite parts consist of alteration products — clilorile, til)n)us lnunlilonde, 

 and serpentine. 



„ 3. — Gahhro. No. 109 x 'l.''. Drawn in ordinary light. Clear pieces 

 with needle-like inclusions are grains of sec(5ndary quartz with apatite. 

 Felspar is partly decomposed, and diallage shows fibrous structure. 



,, 4. — Epidoie Rock. No. 65 x "/'. Drawn in ordinary light. 8h(»ws 

 granular epidote and dark shaded masses of hornl)lende. 



„ 5. — Angen-gneiss. No. 249 x -.A. Drawn in ordinary light, and shows 

 "eyes" of felspar and quartz, and strings of biotite. 



Fig. C. — Fine-grained Gneiss. No. 192 x ■'.?. Drawn in ordinary light. 

 Section at right angles to planes of foliation. Large black mass is a 

 grain of magnetite. Parallel flakes of biotite shaded daik. Colourless 

 grains with well-marked outlines are grains of mica (sericite ?). 



Platk hi. 



Fig. 1. — Gneiss. No. 7G x "'.''. Drawn in ordinary light. .Section parallel to 

 foliation planes. Numerous grains of epidote. 



,, 2. — F/agioc'Iase. No. 147 x ■"..''. Di-awn in ordinary light. Basal cleavage 

 (jf mica well-shown, llest of slide consists of felspar. Extinction of 

 mica and felspar is parallel to cleavage lines of the formei-. 



„ 3. — Arkose. No. 213 x ■".;"'. Drawn in ordinary iiglit. Clear grains are 

 more or less rounded particles of quartz. Shaded portions repi-esent 

 microcline grains. Irregular black patches consist of magnetite and 

 ha-niatite. 



„ 4. — Jllieroe/ine. No. \Sa x •".,"'. Drawn "under crossed nicols." One- 

 half of microcline is extinguished. Strings of pl.igioclase show ajliite 

 twiiniing. 



„ 5. — Flagiflclase. No. 15(? x ".,;'. Drawn "under crossed nicols." One- 

 half of the plagioclase is extinguished. 



,, G. — F/i7gior/ase. No. 15r? x '..''. Drawn " under crossed nicols." Section 

 of plagioclase with associati^d mass of microcline. 



