. The geology of the goldfields of British Guiana. AUGITE GRANITITE, x 18,BLACK CREEK, GROETE CREEK. Phufo ly J. Willinmf. TONALITE, X 18,CABURI, MAZARUNI RIVER. Thijfo ly J. }yUHamf. The retTO(jraphy of the Granitic Rockti. 71 Inchisions in th Granitites—In many places the granitite containsmasses, varying much in size, of the gneissose rocks through which ithas been intruded; these in no way differ in structure and in compositionfrom the rocks they have been derived from. In places, as at Kartabo on the Cuyuni River, masses occur in thegranitite which appear to have been derived from clastic
. The geology of the goldfields of British Guiana. AUGITE GRANITITE, x 18,BLACK CREEK, GROETE CREEK. Phufo ly J. Willinmf. TONALITE, X 18,CABURI, MAZARUNI RIVER. Thijfo ly J. }yUHamf. The retTO(jraphy of the Granitic Rockti. 71 Inchisions in th Granitites—In many places the granitite containsmasses, varying much in size, of the gneissose rocks through which ithas been intruded; these in no way differ in structure and in compositionfrom the rocks they have been derived from. In places, as at Kartabo on the Cuyuni River, masses occur in thegranitite which appear to have been derived from clastic rocks. Therock at Kartabo is coarse-textured, and shows in all parts I haveexamined a more or less laminated structure. Its specific gravityis 2-76. It is made up of a microcrystalline mosaic of quartz, withsome plates of water-clear feldspar, and a few showing plagioclasticmarkings ; traversed by streams of green hornblende lying approximatelyparallel in their long diameters to one another. A few grains ofepidote are also present, and in parts some grains of magnetite arefound. Quartz-mica-diorite.—This rock oc
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