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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datum gravity . The arbitrary reference surface to which corrections are applied.

phenetics . A set of numerical techniques that group taxa based on overall morphologic similarity. Although common in the 1960s and 70s, it is now rarely used. Syn: numerical taxonomy.

assay ton . A weight of 29.1667 grams, used in assaying to represent proportionately the assay value of an ore. Since it bears the same ratio to one milligram that a ton of 2,000 pounds bears to the troy ounce, the weight in milligrams of precious metal obtained from an assay ton of ore equals the number of ounces to the ton. Abbrev: AT.

sapanthracite (sap-an'-thra-cite). Sapropelic coal of anthracitic rank; it is the highest stage in the sapropelic series. Cf: humanthracite.

seismic pulse . The signal generated by an impulsive seismic energy source (explosive, thumper, air gun, sparker, etc.); may include correlated vibroseis sweep signal. "Wavelet" is sometimes used as a synonym.

accordant junction . The joining of two streams or two valleys whose surfaces are at the same level at the place of junction. See also: Playfair's law. Ant: discordant junction. Syn: concordant junction.

histic epipedon . A thin organic soil horizon that is saturated with water at some period of the year unless artificially drained and that is at or near the surface of a mineral soil. The histic epipedon has a maximum thickness depending on the kind of materials in the horizon and the lower limit of organic carbon is the upper limit for the mollic epipedon.

pellodite (pel'-lo-dite). A term used by Schuchert (1924, p.441) for a water-laid sandy varved clay, and by Pettijohn (1957, p.273) for the lithified equivalent of a varved clay. It is apparently an equivalent or variant spelling of pelodite.

eukrite (eu'-krite). Obsolete spelling of eucrite [meteorite].

exocyclic (ex-o-cy'-clic). Said of an irregular echinoid in which the periproct is located outside of the oculogenital ring. Ant: endocyclic.


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