A Summary of Progress in Petrography. in 1887-1896

acid Al,O alteration Amer AMERICAN NATURALIST analysis andesites angle apatite augite axes axis basalt biotite Bull calcite CaO MgO cavities chlorite cleavage Colby University color colorless composed composition corresponds constituents contains crystalline crystals cyanite described diabases diorites dolerite double refraction dykes Edited by Dr epidote eruptive etched Fe,O feldspar former forms Franç gabbros garnet Geol Geological glassy gneiss grains granite green groundmass H₂O hornblende idiomorphic inclusions interesting iron Jour Kryst lava leucite Magazine magma magnetite mass meteoric mica microlites MINERALOGY AND PETROGRAPHY.¹ Mitth monoclinic Na,O nepheline nepheline rocks Neues Jahrb occurring olivine optical original orthoclase orthorhombic Petrographical plagioclase planes porphyritic portion prismatic proustite pseudomorphs pyrargyrite pyrite pyroxene quartz rare mineral regarded result rhombohedral rutile sanidine scapolite schists serpentine silicates specific gravity specimen substance supposed thin sections tion tourmaline twinned parallel varieties veins W. S. Bayley Waterville yielded Zeits