Contact metamorphism
Changes in rock caused by the heat
of a nearby magma body.
Continental drift A hypothesis,
credited largely to Alfred Wegener,
that suggested all present continents
once existed as a single
supercontinent. Further, he posited
that beginning about 200 million
years ago, the supercontinent began
breaking into smaller continents,
which then drifted to their present
positions.
Continental margin See Active
continental margin and Passive
continental margin.
Continental rift A linear zone
along which continental lithosphere
stretches and pulls apart. Its creation
may mark the beginning of a new
ocean basin.
Continental rise The gently
sloping surface at the base of the
continental slope.
Continental shelf The gently
sloping submerged portion of the
continental margin, extending from
the shoreline to the continental
slope.
Continental slope The steep
gradient that leads to the deepocean floor and marks the seaward
edge of the continental shelf.
Continental volcanic arc
Mountains formed in part by
igneous activity associated with the
subduction of oceanic lithosphere
beneath a continent. Examples
include the Andes and the
Cascades.
Convergent plate boundary A
boundary in which two plates move
together, resulting in oceanic
lithosphere being thrust beneath an
overriding plate, eventually to be
reabsorbed into the mantle. It can
also involve the collision of two
continental plates to create a
mountain system.
Core Located beneath the mantle,
it is Earth’ s innermost layer. The
core is divided into an outer core
and an inner core.
Correlation Establishing the
equivalence of rocks of similar age
in different areas.
Covalent bond A chemical bond
produced by the sharing of
electrons.
Crater The depression at the
summit of a volcano, or that which
is produced by a meteorite impact.
Craton That part of the continental
crust that has attained stability; that
is, it has not been affected by
significant tectonic activity during the
Phanerozoic eon. It consists of the
shield and stable platform.
Creep The slow downhill
movement of soil and regolith.
Crevasse A deep crack in the
brittle surface of a glacier.
Cross-bedding Structure in which
relatively thin layers are inclined at
an angle to the main bedding.
Formed by currents of wind or water.
Cross-cutting A principle of
relative dating. A rock or fault is
younger than any rock (or fault)
through which it cuts.
Crust The very thin, outermost
layer of Earth.
Crystal An orderly arrangement
of atoms.
Crystal shape See Habit.
Crystalline texture See Nonclastic.
Crystallization The formation
and growth of a crystalline solid
from a liquid or gas.
Curie point The temperature
above which a material loses its
magnetization.
Cut bank The area of active
erosion on the outside of a meander.
Cutoff A short channel segment
created when a river erodes through
the narrow neck of land between
meanders.
Dark silicate Silicate minerals
containing ions of iron and/or
magnesium in their structure. They
are dark in color and have a higher
specific gravity than
nonferromagnesian silicates.
Daughter product An isotope
resulting from radioactive decay.
Debris flow A relatively rapid
type of mass wasting that involves a
flow of soil and regolith containing a
large amount of water; also called
mudflows.
Debris slide See Rockslide.
Decompression melting Melting
that occurs as rock ascends due to a
drop in confining pressure.
Deep-focus earthquake An
earthquake focus at a depth of more
than 300 kilometers.
Deep-ocean basin The portion of
seafloor that lies between the
continental margin and the oceanic
ridge system. This region comprises
almost 30 percent of Earth’ s surface.
Deep-ocean trench See Trench.
Deflation The lifting and removal
of loose material by wind.
Deformation General term for
the processes of folding, faulting,
shearing, compression, or extension
of rocks as the result of various
natural forces.
Delta An accumulation of
sediment formed where a stream
enters a lake or ocean.
Dendritic drainage pattern A
stream system that resembles the
pattern of a branching tree.
Density The weight per unit
volume of a particular material.
Desert One of the two types of
dry climate; the drier of the dry
climates.
Desert pavement A layer of
coarse pebbles and gravel created
when wind removes the finer
material.
Detachment fault A low-angle
fault that represents a major
boundary between unfaulted rocks
below that exhibit ductile
deformation and rocks above that
exhibit brittle deformation via
faulting.
Detrital sedimentary rocks Rocks
that form from the accumulation of
materials that originate and are
transported as solid particles derived
from both mechanical and chemical
weathering.
Diagenesis A collective term for
all the chemical, physical, and
biological changes that take place
after sediments are deposited and
during and after lithification.
Dike A tabular-shaped intrusive
igneous feature that cuts through
the surrounding rock.
Dip The angle at which a rock
layer is inclined from the horizontal.
The direction of dip is at a right
angle to the strike.
Dip-slip fault A fault in which
the movement is parallel to the dip
of the fault.
Discharge The quantity of water
in a stream that passes a given point
in a given period of time.
Disconformity A type of
unconformity in which the beds
above and below are parallel.
Discontinuity A sudden change
with depth in one or more of the
physical properties of the material
making up Earth’ s interior. The
boundary between two dissimilar
materials in Earth’ s interior as
determined by the behavior of
seismic waves.
Discordant A term used to
describe plutons that cut across
existing rock structures, such as
bedding planes.
Disseminated deposit Any
economic mineral deposit in which
the desired mineral occurs as
scattered particles in the rock but in
sufficient quantity to make the
deposit an ore.
Dissolved load The portion of a
stream’ s load carried in solution.
Distributary A section of a stream
that leaves the main flow.
Diurnal tide A tide characterized
by a single high and low water
height each tidal day.
Divergent plate boundary A
boundary in which two plates move
apart, resulting in upwelling of
material from the mantle to create
new seafloor.
Divide An imaginary line that
separates the drainage of two
streams; often found along a ridge.
Dome A roughly circular,
upfolded structure.
Drainage basin The land area
that contributes water to a stream.
Drawdown The difference in
height between the bottom of a cone
of depression and the original height
of the water table.
Drift See Glacial drift.
Drumlin A streamlined
asymmetrical hill composed of
glacial till. The steep side of the hill
faces the direction from which the
ice advanced.
Dry climate A climate in which
the yearly precipitation is less than
the potential loss of water by
evaporation.
Ductile deformation A type of
solid-state flow that produces a
change in the size and shape of a
rock body without fracturing.
Occurs at depths where
535
GLOSSARY
Changes in rock caused by the heat
of a nearby magma body.
Continental drift A hypothesis,
credited largely to Alfred Wegener,
that suggested all present continents
once existed as a single
supercontinent. Further, he posited
that beginning about 200 million
years ago, the supercontinent began
breaking into smaller continents,
which then drifted to their present
positions.
Continental margin See Active
continental margin and Passive
continental margin.
Continental rift A linear zone
along which continental lithosphere
stretches and pulls apart. Its creation
may mark the beginning of a new
ocean basin.
Continental rise The gently
sloping surface at the base of the
continental slope.
Continental shelf The gently
sloping submerged portion of the
continental margin, extending from
the shoreline to the continental
slope.
Continental slope The steep
gradient that leads to the deepocean floor and marks the seaward
edge of the continental shelf.
Continental volcanic arc
Mountains formed in part by
igneous activity associated with the
subduction of oceanic lithosphere
beneath a continent. Examples
include the Andes and the
Cascades.
Convergent plate boundary A
boundary in which two plates move
together, resulting in oceanic
lithosphere being thrust beneath an
overriding plate, eventually to be
reabsorbed into the mantle. It can
also involve the collision of two
continental plates to create a
mountain system.
Core Located beneath the mantle,
it is Earth’ s innermost layer. The
core is divided into an outer core
and an inner core.
Correlation Establishing the
equivalence of rocks of similar age
in different areas.
Covalent bond A chemical bond
produced by the sharing of
electrons.
Crater The depression at the
summit of a volcano, or that which
is produced by a meteorite impact.
Craton That part of the continental
crust that has attained stability; that
is, it has not been affected by
significant tectonic activity during the
Phanerozoic eon. It consists of the
shield and stable platform.
Creep The slow downhill
movement of soil and regolith.
Crevasse A deep crack in the
brittle surface of a glacier.
Cross-bedding Structure in which
relatively thin layers are inclined at
an angle to the main bedding.
Formed by currents of wind or water.
Cross-cutting A principle of
relative dating. A rock or fault is
younger than any rock (or fault)
through which it cuts.
Crust The very thin, outermost
layer of Earth.
Crystal An orderly arrangement
of atoms.
Crystal shape See Habit.
Crystalline texture See Nonclastic.
Crystallization The formation
and growth of a crystalline solid
from a liquid or gas.
Curie point The temperature
above which a material loses its
magnetization.
Cut bank The area of active
erosion on the outside of a meander.
Cutoff A short channel segment
created when a river erodes through
the narrow neck of land between
meanders.
Dark silicate Silicate minerals
containing ions of iron and/or
magnesium in their structure. They
are dark in color and have a higher
specific gravity than
nonferromagnesian silicates.
Daughter product An isotope
resulting from radioactive decay.
Debris flow A relatively rapid
type of mass wasting that involves a
flow of soil and regolith containing a
large amount of water; also called
mudflows.
Debris slide See Rockslide.
Decompression melting Melting
that occurs as rock ascends due to a
drop in confining pressure.
Deep-focus earthquake An
earthquake focus at a depth of more
than 300 kilometers.
Deep-ocean basin The portion of
seafloor that lies between the
continental margin and the oceanic
ridge system. This region comprises
almost 30 percent of Earth’ s surface.
Deep-ocean trench See Trench.
Deflation The lifting and removal
of loose material by wind.
Deformation General term for
the processes of folding, faulting,
shearing, compression, or extension
of rocks as the result of various
natural forces.
Delta An accumulation of
sediment formed where a stream
enters a lake or ocean.
Dendritic drainage pattern A
stream system that resembles the
pattern of a branching tree.
Density The weight per unit
volume of a particular material.
Desert One of the two types of
dry climate; the drier of the dry
climates.
Desert pavement A layer of
coarse pebbles and gravel created
when wind removes the finer
material.
Detachment fault A low-angle
fault that represents a major
boundary between unfaulted rocks
below that exhibit ductile
deformation and rocks above that
exhibit brittle deformation via
faulting.
Detrital sedimentary rocks Rocks
that form from the accumulation of
materials that originate and are
transported as solid particles derived
from both mechanical and chemical
weathering.
Diagenesis A collective term for
all the chemical, physical, and
biological changes that take place
after sediments are deposited and
during and after lithification.
Dike A tabular-shaped intrusive
igneous feature that cuts through
the surrounding rock.
Dip The angle at which a rock
layer is inclined from the horizontal.
The direction of dip is at a right
angle to the strike.
Dip-slip fault A fault in which
the movement is parallel to the dip
of the fault.
Discharge The quantity of water
in a stream that passes a given point
in a given period of time.
Disconformity A type of
unconformity in which the beds
above and below are parallel.
Discontinuity A sudden change
with depth in one or more of the
physical properties of the material
making up Earth’ s interior. The
boundary between two dissimilar
materials in Earth’ s interior as
determined by the behavior of
seismic waves.
Discordant A term used to
describe plutons that cut across
existing rock structures, such as
bedding planes.
Disseminated deposit Any
economic mineral deposit in which
the desired mineral occurs as
scattered particles in the rock but in
sufficient quantity to make the
deposit an ore.
Dissolved load The portion of a
stream’ s load carried in solution.
Distributary A section of a stream
that leaves the main flow.
Diurnal tide A tide characterized
by a single high and low water
height each tidal day.
Divergent plate boundary A
boundary in which two plates move
apart, resulting in upwelling of
material from the mantle to create
new seafloor.
Divide An imaginary line that
separates the drainage of two
streams; often found along a ridge.
Dome A roughly circular,
upfolded structure.
Drainage basin The land area
that contributes water to a stream.
Drawdown The difference in
height between the bottom of a cone
of depression and the original height
of the water table.
Drift See Glacial drift.
Drumlin A streamlined
asymmetrical hill composed of
glacial till. The steep side of the hill
faces the direction from which the
ice advanced.
Dry climate A climate in which
the yearly precipitation is less than
the potential loss of water by
evaporation.
Ductile deformation A type of
solid-state flow that produces a
change in the size and shape of a
rock body without fracturing.
Occurs at depths where
535
GLOSSARY