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.

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elevator tectonics (el'-e-va''-tor). A rarely used term introduced by Dietz and Holden (1966, p.353) for the rise and fall of blocks of sialic crust from surficial to abyssal levels or vice versa.

hypogastralium (hy''-po-gas-tra'-li-um). A specialized sponge spicule lying largely beneath the endopinacoderm of the spongocoel.

wurtzilite (wurtz'-i-lite). A black, massive asphaltic pyrobitumen, sectile and infusible, that is closely related to uintahite, but insoluble in turpentine, and derived from the metamorphism of petroleum. It is found in veins in Uinta County in Utah.

Thornthwaite's classification (Thorn'-thwaite's). A climate classification, formulated by the U.S. agricultural climatologist Warren Thornthwaite, that is based on ratios of precipitation to evaporation. Five humidity provinces are distinguished: perhumid, humid, subhumid, semiarid, and arid. Cf: Köppen's classification.

polkanovite . A metallic hexagonal mineral: Rh12As7.

facies-departure map . A facies map based on the degree of similarity to some particular sedimentary rock composition (optimum facies or single-component end member). Term suggested by Forgotson (1960, p.94) to replace distance-function map.

concave bank (con-cave'). The outer bank of a curved stream, with the center of the curve toward the channel; e.g. an undercut slope. Ant: convex bank.

corn snow . Spring snow consisting of large, wet crystals.

divisional plane (di-vi'-sion-al). A general term that includes joints, cleavage, faults, bedding planes, and other surfaces of separation.

crenulation lineation . A lineation defined by the hinges of small folds (crenulations) associated with crenulation cleavage .

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