[Geologic age]—the age of an object as stated in terms of [geologic time] (e.g., a Pennsylvanian fern, Cretaceous dinosaur).
[Geologic time]—all time which has elapsed since the first known [rocks] were formed and continuing until recent, or modern, times.
[Geologic time scale]—record of the divisions of earth history.
[Gypsum]—a [mineral], hydrated calcium sulfate (CaSO₄·2H₂O). See [Anhydrite].
[Hoodoo]—a form produced by erosion of [rock].
[Ice age]—the [Pleistocene] [Epoch] of the Quaternary [Period], [Cenozoic] [Era]; a time of extensive glaciation.
[Igneous rock]—[rocks] which have solidified from lava or molten rock called magma.
[Joint]—a fracture in a [rock] along which there has been no displacement on opposite sides of the break.
[Joint System]—a series of two or more sets of [joints] passing through a [rock] mass and separating it into blocks of more or less regular pattern.
[Mass-wasting]—erosion caused chiefly by gravity.