Aids in Practical Geology

acid altered ambulacral andesites angles aperture appear areas assay augite axis basal bead become biotite brown calcareous calcite carbonate Carboniferous character CHARLES GRIFFIN cleavage colour colourless common commonly constituents convex Cretaceous crossed nicols crystalline crystals developed Devonian EDITION Engineer eurites examined EXETER STREET fairly felspar flame foliated fossils fragments genera Geol glass Gotlandian grains granite granular granules green groundmass Handsome Cloth head-shield hinge-line hornblende igneous rocks iron Jurassic lavas leucite limestones lobes magnetite margin marked mass mica microscope minerals mouth numerous observed occur olivine opaque ophitic optic ordinary Ordovician orthoclase outer oxide parallel Plagioclase planes plates pleochroism polarised porphyritic posterior powder PRACTICAL prisms Prof pygidium pyroxene quartz radial reaction Refr refractive rhyolites ribs rotation sections seen septa shell side silica soda sometimes specific gravity specimens spherulites structure sulphur surface Suture-lines trace trachytic tube types typical umbo valve ventral whorl