. The geology of the goldfields of British Guiana. rocks fromaplite, through granite and granitite, to rocks approximatingin composition to syenite and to diorite. Basic Secretions in the Granitites—In certain of the masses of thegranitites segregation-patches occur which are of much darker colourand of higher specific gravity than the bulk of the rock. The patchesare, as a rule, of finer grain and closer texture than the rock from whichthey have segregated. They consist of plates of oligoclase with inclu-sions of sericite and epidote, some plates of orthoclase, and a few patchesof microcline;

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. The geology of the goldfields of British Guiana. rocks fromaplite, through granite and granitite, to rocks approximatingin composition to syenite and to diorite. Basic Secretions in the Granitites—In certain of the masses of thegranitites segregation-patches occur which are of much darker colourand of higher specific gravity than the bulk of the rock. The patchesare, as a rule, of finer grain and closer texture than the rock from whichthey have segregated. They consist of plates of oligoclase with inclu-sions of sericite and epidote, some plates of orthoclase, and a few patchesof microcline; irregular areas of quartz, many of which show strain-shadows ; many plates of brown biotite, some of chlorite secondary tobiotite, and many of green hornblende, with some granules of crystals and some grains of sphene, with grains and minutecrystals of magnetite, and of titaniferous iron ore, and a few small prismsof apatite are present as accessories. These basic secretions approachin composition t(j quartz-mica-diorite. AUGITE GRANITITE, x 18,BLACK CREEK, GROETE CREEK. Phufo ly J. Willinmf

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Keywords: ., bookcentury1900, bookdecade1900, booksubjectgeology, booksubjectp