drop [coal] . In the roof of a coal seam, a funnel-shaped downward intrusion of sedimentary rock, usually sandstone. Cf: stone intrusion.
GeoWord of the Day
The GeoWord of the Day is a free service of the American Geosciences Institute. All of the terms and definitions are from the Glossary of Geology, 5th Edition Revised.
polar-orbiting satellite . A satellite in relatively low orbit that travels near the geographical poles on meridional trajectories. Earth rotates through the plane of the satellite's orbit. The altitude of the satellite's orbit is about 800 to 1,000 km (500 to 620 mi).
stratophenetics (strat''-o-phe-net'-ics). That method in systematics wherein ancestor-descendant (phylogenetic or evolutionary) relationships among taxa are inferred from comparison of morphologic, anatomic, and any other observable characteristics of fossils when the fossils are arranged according to their geochronologic ages or stratigraphic horizons. Cf: phenetics.
liquid fractionation . Generation of a compositionally graded column of magma through the buoyancy-driven gravitational segregation of differentiated liquids along the margins of an active body (McBirney et al., 1985). Liquids may be generated by boundary layer crystallization or wall-rock melting. See also: sidewall crystallization; compositional convection .
endokinetic (en''-do-ki-net'-ic). Said of a fissure in a rock that is the result of strain within the rock unit itself. Archaic. Cf: exokinetic.
intertonguing (in-ter-tongu'-ing). The disappearance of sedimentary bodies in laterally adjacent masses owing to splitting into many thin tongues, each of which reaches an independent pinch-out termination; the intergradation of markedly different rocks through a vertical succession of thin interlocking or overlapping wedge-shaped layers. Syn: interfingering; interdigitation.
underlapping faults . Two subparallel , noncollinear faults with traces that do not extend past each other (Peacock et al., 2000). Cf: overlapping faults.
Ustox . Oxisols that have an ustic moisture regime and either hyperthermic or isohyperthermic soil temperature regimes or have < 20 kg organic carbon in the surface cubic meter. A suborder in the U.S. system of soil taxonomy.
parakhinite . A dark green trigonal mineral: Cu2+3PbTe6+O6(OH)2. It is a dimorph of khinite.
meandering valley . A valley having a pattern of successive windings broadly resembling the trace of a meandering stream. The windings, or valley meanders, are of the same general order of size. Many are relict former channels of much larger rivers, such as glacial meltwater rivers. Cf: underfit stream.
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