bar (stream) - An accumulation of sediment, usually sandy, which forms at the borders or in the channels of streams or offshore from a beach.
barchan - A crescent-shaped sand dune moving across a clean surface with its convex face upwind and its concave slip face downwind.
archean, archaean - An eon of geologic time extending from about 3800 to 2500 million years ago. The Archean eon is divided into four eras: Eoarchean, Paleoarchean, Mesoarchean, and Neoarchean.
barrier island - A long, narrow island parallel to the shore, composed of sand and built by wave action.
basalt - A fine-grained, dark, mafic igneous rock (~50% Si O) composed largely of plagioclase feldspar and pyroxene; rough volcanic equivalent of gabbro.
alkaline - Term pertaining to a highly basic, as opposed to acidic, substance.
For example, hydroxide or carbonate of sodium or potassium.
anorthosite - An igneous rock predominantly composed of plagioclase feldspar (90–100%), and a minimal mafic component (0–10%).
Anorthosites constitute the light-colored areas of the Moon's surface.
Thus water in the well rises above the surrounding water table.
asphalt - A dark bituminous substance found in natural beds. asthenosphere - The highly viscous, mechanically weak region of the upper mantle of the Earth that lies below the lithosphere at depths between 100 and 200 km below the surface.
angle of repose - The steepest slope angle in which particular sediment will lie without cascading down.
angstrom - A length of 10 meter or one hundred millionth of a centimeter. angular unconformity - An unconformity in which the bedding planes of the rocks above and below are not parallel.
astrobleme - A circular erosional feature that has been ascribed to the impact of a meteorite or comet.