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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rheology (rhe-ol'-o-gy). The study of the deformation or flow of matter and the relationship between stress and strain and the responses of rock to deformation, including elastic, brittle, viscous, and plastic behaviors.

cala [coast] (ca'-la). A short, narrow ria formed in a limestone coast; a small semicircular shallow bay along a cala coast, as along the coast of Majorca. Etymol: Spanish, "cove, small bay, inlet". See also: caleta [coast].

gauge pressure . Pressure above one atmosphere.

greenstone [sed] . A compact, nonoolitic, relatively pure chamosite mudstone interbedded with oolitic ironstone in the Lower Jurassic of Great Britain.

balance year . The period from the time of minimum mass in one year to the time of minimum mass in the succeeding year for a glacier; the period of time between the formation of one summer surface and the next. See also: net balance. Syn: budget year.

artesian province . A region within which structure, stratigraphy, topography, and climate combine to produce conditions favorable to the existence of one or more artesian aquifers; e.g. the Atlantic and Gulf Coastal Plain.

double tombolo . Two separate bars or barriers connecting an island (usually of large extent and close to the shore) with the mainland. Cf: tombolo.

Laue group . One of eleven subsets of the 32 crystal classes, obtained by adding a center of symmetry to each class. This is the symmetry of the weighted reciprocal lattice , except in cases where Friedel's law is violated by the effects of anomalous dispersion.

Tremadocian (Tre-ma-do'-cian). A series or stage of the Standard Global Chronostratigraphic Scale: lowermost Ordovician (above Cambrian). The basal GSSP is in Newfoundland (Cooper et al., 2001). Also spelled: Tremadoc.

Cambrian evolutionary fauna . The classes of marine invertebrates which account for the bulk of marine diversity during the Cambrian Period, includes trilobites, inarticulate brachiopods, and monoplacophoran molluscs.