transverse ripple . A ripple formed approximately at right angles to the direction of the current. Its profile may be asymmetric or symmetric.
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.
polystromatic (pol''-y-stro-mat'-ic). Said of a plant part, e.g. an algal thallus, composed of many layers of cells. Cf: monostromatic; oligostromatic.
fiamme (fi-am'-me). Dark, vitric lenses in welded tuffs, averaging a few centimeters in length, perhaps formed by the collapse of fragments of pumice. The presence of fiamme may be called flame structure [pyroclast]. Etymol: Pl. of Italian "fiamma", "flame". Cf: piperno.
membraniporiform (mem''-bra-ni-por'-i-form). Said of a generally unilaminate encrusting colony in cheilostome bryozoans, firmly attached by calcified or membranous walls of zooids (Lagaaij and Gautier, 1965, p.51).
quartz diorite . (a) In the IUGS classification, a plutonic rock with Q between 5 and 20, P/(A+P) greater than 90, and plagioclase more sodic than An50. (b) A group of plutonic rocks having the composition of diorite but with an appreciable amount of quartz, i.e. between 5 and 20 percent of the light-colored constituents, according to Streckeisen (1967, p.157); also, any rock in that group; the approximate intrusive equivalent of dacite. Quartz diorite grades into granodiorite as the alkali feldspar content increases. Syn: quartz-bearing diorite.
crinozoan (cri-no-zo'-an). Any attached echinoderm belonging to the subphylum Crinozoa, characterized by a partial meridional growth pattern tending to produce an aboral cup-shaped or globoid plated theca and a partial radially divergent growth pattern forming appendages. Among the major groups included in the subphylum are blastoids, crinoids, and cystoids.
sporite (spo'-rite). A coal microlithotype containing 95% or more of sporinite.
pseudovolcano (pseu''-do-vol-ca'-no). A large crater or circular hollow believed not to be associated with volcanic activity; e.g. a crater that is possibly meteoritic in origin but may be the result of phreatic explosion or cauldron subsidence. Adj: pseudovolcanic.
segregated vein . A fissure whose mineral filling is derived from the country rock by the action of percolating water. Syn: exudation vein. Cf: infiltration vein. See also: lateral secretion.
sporangium (spo-ran'-gi-um). An organ within which spores are produced and borne until their release; e.g., a pollen sac of a gymnosperm, an anther of an angiosperm, or the saclike structure in Fungi that produces spores endogenously. Pl: sporangia. Cf: megasporangium; microsporangium. Obsolete syn: spore case.
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