Argentiferous. Containing silver.
Argillaceous. Clayey.
Articulata. A natural division of animals having their limbs articulated or jointed together, like the lobster.
Asaphus. An obscure genus of trilobites.
Asbestus. A fibrous mineral of which an incombustible cloth is sometimes made.
Asterolepis. (Gr., star scale). It is the largest fish yet found in the Old Red Sandstone.
Augite. (Gr., luster)—a mineral.
Basalt. An igneous rock, often columnar and supposed to be ancient volcanic lava. It is the most common of the group called Trap-rocks.
Bed or Stratum. A layer of material the whole of which exhibits some common character.