248 



B. KOTO 



microscopic bodies are mostly found imbedded in quartz. The pri- 

 mary muscovife, though subordinate in quantity to that of biotite, 

 still forms a constant component. It is usually resolved into loose 

 folige, and occurs often interlaced with bleached, green, fibrous biotite. 



Accessory minerals are zircon, and a cherry-red garnet, Avhioh 

 never occurs with crystallographic outlines, but usually in rather large 

 o-rains, lapped and encircled by the lamellae of biotite. It contains in 

 it manv l3rown scales of magnesia mica, gas-pores in the form of 

 dodecadedra, and also colourless grains which are usually supposed to 

 be of a quartzose nature. The garnet was observed microscopically in 

 nearly all the slides examined; it may, therefore, be looked upon as 

 a characteristic accessory C(:)mponent, and this fact makes some of 

 the rocks of this group appi'oach more closely to a genuine granulite. 



Among the various modifications, the following are the principal 

 types : — gneiss-mica sclust, two-mica schist, garnet -hiotite schist, and 

 hornblende-hiotite schist. 



A a) Gneiss- Mica- Schist. 



Scaly, light-grey, thick tabular schist with the plane- parallel 

 structure, being made up of quartz, orthoclase, plagioclase, and biotite. 

 The last mineral is arranged approximately in one plane, alternating 

 with the quartz-feldsp:jr aggregates. The four components are all 

 nearly of the same size (1 mm.), and the weathered rock appears not 

 unlike a micaceous sandstone. The quartz and feldspars are present 

 in equal quantities, the former is often partially or wholly enclosed hy 

 orthoclase. The liquid-inclusions with the condensed carbonic acid 

 and bubbles are abundant in the quartz, being disposed in chains ; 

 other enclosures are round, tombac-brown biotite, clumps of the 

 opaque iron-glance, and only a few grains and prisms of zircon. 



