Anticline. An upward [fold] or elongated arch in rock layers.
Aquifer. A rock layer that is water-bearing.
Artesian water. Groundwater that is under sufficient pressure to rise above the level at which it is encountered in a well. It does not necessarily rise completely to the surface.
Basalt. An extrusive igneous rock, fine-grained and dark colored, composed mainly of calcium-rich [feldspar] and the black mineral pyroxene.
Basement. A name commonly applied to metamorphic or [igneous rocks] underlying the sedimentary rock layers.
Batholith. A large body of intrusive igneous rock, 40 square miles or more in outcrop area, which extends downward to an unknown depth.
Bedrock. The solid rock which underlies soil, sand, clay, or other loose surface material.
Belemnite. The cigar-shaped internal shell of an extinct marine [mollusk] similar to a squid.
Brachiopod. One of a large group of marine shelled animals having two unequal, bilaterally symmetrical shells.
Bryozoa. A large group of tiny colonial marine animals that secrete calcareous or horny coverings in a great variety of shapes.