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GLOSSARY
A
Aa A type of lava flow that has a jagged, blocky surface.
Abrasion The grinding and scraping of a rock surface by the friction and impact of rock
particles carried by water, wind, or ice.
Active continental margin Usually narrow and consisting of highly deformed sediments, they
occur where oceanic lithosphere is being subducted beneath the margin of a continent.
Angular unconformity An unconformity in which the older strata dip at an angle different from
that of the younger beds.
Anticline A fold in sedimentary strata that resembles an arch.
Asthenosphere A subdivision of the mantle situated below the lithosphere. This zone of weak
material exists below a depth of about 100 km and in some regions extends as deep as 700
kilometers. The rock within this zone is easily deformed.
Atmosphere The gaseous portion of a planet; the planet’s envelope of air. One of the traditional
subdivisions of Earth’s physical environment.
B
Basalt An aphanitic igneous rock of mafic composition.
Basaltic Term used to describe igneous rocks that contain abundant dark (ferromagnesian)
minerals and about 50 percent silica.
Batholith A large mass of igneous rock that formed when magma was emplaced at depth,
crystallized, and was subsequently exposed by erosion.
Bedding plane A nearly flat surface separating two beds of sedimentary rock. Each bedding
plane marks the end of one deposit and the beginning of another having different characteristics.
Bedrock A general term for the rock that underlies soil or other unconsolidated surface
materials.
Breccia A sedimentary rock composed of angular fragments that were lithified.
C
Caldera A large depression typically caused by collapse of the summit area of a volcano
following a violent eruption.
Cap rock A necessary part of an oil trap, the cap rock is impermeable and hence keeps upwardly
mobile oil and gas from escaping at the surface.
Capacity The total amount of sediment a stream is able to transport.
Carrier beds are rock layers that are very permeable and transmit fluids.
Cavern A naturally formed underground chamber or series of chambers most commonly
produced by solution activity in limestone.
Chemical weathering The processes by which the internal structure of a mineral is altered by
the removal and/or addition of elements.