Biostratigraphic dating relies on

arroyo - A steep-sided and flat-bottomed gully in an arid region that is occupied by a stream only intermittently, after rains.artesian well - A well that penetrates an impermeable layer of rock to reach an aquifer containing water under pressure.

alkali metal - A strongly basic metal like potassium or sodium.

Geological analysis relies mainly on chemistry, physics and mathematics. a'a' lava - basaltic lava characterized by a rough or rubbly surface composed of broken lava blocks called clinker.

A-horizon - The uppermost layer of a soil, containing organic material and leached minerals.

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.