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.arkose - A variety of sandstone containing abundant feldspar and quartz, frequently in angular, poorly sorted grains.allochthonous - Refers to something formed elsewhere than its present location. alluvial fan - An alluvial fan is a triangular-shaped deposit of sediment at the point where a river emerges from a mountainous area and flows onto a more gently sloping plain.alluvium - Sediment of sorted or unconsolidated sand, gravel, and clay that has been deposited by flowing water.astrobleme - A circular erosional feature that has been ascribed to the impact of a meteorite or comet.
bank - The land alongside or sloping down to a river or lake.
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.
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.
anorthosite - An igneous rock predominantly composed of plagioclase feldspar (90–100%), and a minimal mafic component (0–10%).