steam vent . A type of hot spring from which superheated steam is rapidly and violently expelled.

river flat . An alluvial flat adjacent to a river; a bottom.

multidomains . In a ferromagnetic , ferroelastic , or ferroelectric crystal, a region consisting of many single domains. Cf: single domains.

Gaussian distribution (Gauss'-i-an). A bell-shaped distribution based on two parameters, the mean and the standard deviation . The distribution characterizes repeated measurements, subject to random, additive errors, and has a fundamental place in parametric statistics. Named for Karl Friedrich Gauss (1777-1855), German mathematician. Syn: normal distribution .

crust [volc] . The outer part of a lava flow that has solidified after losing heat to the exterior (Kilburn, 2000).

hemidisc (hem'-i-disc). A sponge spicule consisting of an unequal-ended amphidisc.

genetic (ge-net'-ic). Pertaining to relationships due to a common origin, or to features involving genes or gene complexes.

cluster (clus'-ter). A group of criss-crossing dikes demonstrably related to an exposed pluton. Cf: dike swarm; dike set.

pyroxene-perthite (py'-rox-ene-perth'-ite). Lamellar intergrowths of any of several pyroxenes, as with the feldspars.

deltaic coastal plain . A coastal plain composed of a series of coalescing deltas; it consists initially of natural levee ridges separated by basins.