Fold. A bend in rock layers.
Foraminiferida. One-celled marine animals with microscopic, perforated, many-chambered calcium carbonate shells, often called forams.
Fossil. The remains or traces of an animal or plant which has been preserved in the rock.
Fusulinid. One-celled marine animals (forams) with shells which look like a grain of wheat in shape and size, frequently abundant in Colorado Pennsylvanian rocks.
Galena. A heavy gray metallic mineral (PbS), often cubic in form, that is the most important ore of lead.
Gangue. Nonvaluable minerals occurring in [veins] with ore minerals.
Glaciation. Alteration of the earth’s surface by erosion and deposition by [glacier] ice.
Glacier. A body of ice originating on land by recrystallization of snow, and showing evidence of movement by flowing.
Gneiss. A coarse-grained [metamorphic rock] usually banded with streaks of darker, finer-grained rock.
Granite. An intrusive igneous rock consisting essentially of sodium or potassium [feldspar] and quartz, often speckled with dark-colored minerals.