94 HORN EXPEDITION — PETROLOGY. 



EXPLANATION OF PLATES. 



Plate I. 



Fig. 1. — Micro-pegmatite. No. 220 x y.* Section drawn in ordinary light 

 shows a few clear quartz grains, several " cloudy " pieces of felspar, and 

 two large black patches of hceniatite and magnetite. The rest of the rock 

 exhibits the irregular network of quartz and felsjjar of the micro- 

 pegmatite grains, the latter constituent being shaded. 



,, 2. — Micro-pegmatite. No. 215 x "'^ . Drawn in ordinary light. Micro- 

 pegmatitic structure very fine, scarcely shown at all in this figure. Shaded 

 portions are more or less decomposed, felspar crystals usually surrounded 

 by the radiating inclusions. Faint lines have been drawn to indicate the 

 boundaiies of the grains of micro-pegmatite, although these are only to 

 be made out under " crossed nicols." 



,, 3. — Granulitic Pyroxene Diorite. No. 25 x ^/. Felspars are coloui-less, 

 with inclusions. Augite, both porphyritic crystals and small gi'ains 

 shown by light shading. Small grains of hypersthene shown by a little 

 deeper shading. Hornblende by deeper shading. Numerous grains of 

 magnetite shown black. 



,, 4. — Diorite. No. 32 x 'A/'. Drawn in oi-dinary light. Felspar clear. 

 Hornblende shaded. Mass of comminuted augite shown at the bottom 

 of the section. 



„ b.^Diorite. No. 19 x %'. Drawn in ordinary light. Felspar clear. 

 Augite grains indicated by stippling. Hornblende shaded to indicate 

 pleochroisra. 



„ 6. — Uralitic ampliibolite. No. 123 x '.;''. Drawn in ordinary light. 



Plate II. 



Fig. 1. — Olivine Dolerite. No. 195 x ".;\ Drawn in ordinary light. Augite 

 exhibits ophitic structure. Olivine much cracked with magnetite in 

 filling cracks. 



*Thf iiuiuerator of this expression indicates the magnityinii power of the eye-piece and objective used in 

 maliin},' the drawing ; but as the iniajje produced is reduced in the drawing one-third of its real size, the absolute 

 degree of niaijnilication of the minerals of the slide, as represented by the drawing, is denoted by the quotient. 



