Aplite Dikes - A light-colored, fine-grained intrusive igneous rock having a similar
mineralogy to granite.
Batholith - A large, discordant, intrusive body of igneous rock.
Body Fossil - The remains of an ancient organism such as a shell or bones.
Craton - The stable interior portions of continents. Cratons are regions which have not
been deformed for a prolonged period.
Cross-bedding - Bedding laid down at an angle to the horizontal, as in many sand dunes.
Cross-cutting relationships - Geologic realtionships that suggest relative ages: A
geologic feature is younger than the feature it crosses. Thus, a fault cutting across a
rock is younger than the rock.
Dike - A tabular body of igneous rock that cuts across the structure (discordant) of
adjacent rocks or through massive rock.
Dip (as in strike and dip) - The angle a plane (e.g. sedimentary bed, metamorphic foliation,
fault surface) makes with the horizontal plane. The dip-direction is perpendicular to the strike.
Exfoliation - Large, dome-shaped structure, usually composed of granite, formed by sheeting.
Fault - A rupture in ground rock along which there has been differential movement of
the rock on either side.
Foliation - A planar arrangement of minerals or structural features in metamorphic and
igneous rocks.
Fossil - Any preserved remian or trace of animal, plant, or other life form the past.
Gneiss - a foliated metamorphic rock consisting of alternating bands of light (feldspar)
and dark (biotite) minerals.
Granite - A plutonic igneous rock consisting primarily of quartz (20-60%), feldspar, and mica
(biotite/muscovite).
Granodiorite - A plutonic igneous rock containing quartz, plagioclase, and potassium feldspar;
with biotite, hornblende, or more rarely pyroxene as the mafic component.
Limestone - A sedimentary rock composed mostly of the mineral calcite, CaC03.
Migmatite - A composite rock composed of igneous and metamorphic materials, the
result of partial melting at the upper limit of metamorphism.
Monzonite - A plutonic igneous rock consisting of equal amounts of orthoclase and plagioclase,
with little or no quartz, with augite (clinopyroxene) commonly as the mafic mineral.
Mud cracks - Cracks, generally polygonal, caused by the shrinking of a deposit of clay
or silt due to evaportation of watersurface conditions.
Nonconformity - An unconformity (erosional surface) developed between
sedimentary rocks and older rocks (plutonic igneous or metamorphic rocks) that had
been exposed to erosion before the overlying sedimentary rocks exposed them.
Normal fault - A dip-slip fault where the hanging wall has moved down relative to the footwall.
Ouachita orogeny - The continent-continent collision between North America and South
America during the late Paleozoic.
Proterozoic - An eon ranging in time between 2500 million years ago to 570 million years ago.
Protolith - The parent rock (pre-metamorphosis) to a metamorphic rock.
Pseudotachylite - A dark gray or black rock that texturally resembles volcanic glass
(tachylite). Typically forms from high-grade dynamic metamorphism.
Relative time - Dating of rocks and geologic events by their positions in chronological
order without reference to number of years before the present.
Reverse fault - a dip-slip fault where the hanging wall has moved up relative to the footwall.
Ripple marks - Wave-like sedimentary structures produced by wind or water moving
across deposits of sand or silt.
Sandstone - A medium-grained, clastic sedimentary rock.
Schist - A metamorphic rock characterized by a well-developed wavy foliation.
Common minerals include muscovite and biotite.
Sill - A tabular igneous rock that parallels the structure (concordant) of adjacent rocks.
Striations - Scratches or small channels gouged by glacier action or fault slip. Striations
along bedrock indicate direction of ice or direction a fault has moved.
Strike - Compass direction of a horizontal line on a plane (e.g. sedimentary bed, metamorphic
foliation, fault surface).
Strike-slip fault (transcurrent fault) - A fault on which the movement is parallel to the fault's strike.
Thrust fault - a reverse fault that typically dips much less than 45° in which the hanging wall has moved up relative
to the footwall.
Trace Fossil - A sedimentary structure consisting of a fossilized track, trail, burrow, tube or tunnel
resulting from the activities of ancient animal.
Xenolith(inclusion) - A fragment of older rock caught up in an igneous rock.
