Fault of radiometric dating
alkaline - Term pertaining to a highly basic, as opposed to acidic, substance.
For example, hydroxide or carbonate of sodium or potassium.
A-horizon - The uppermost layer of a soil, containing organic material and leached minerals.
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.
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.