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.

dicyclic (di-cy'-clic). (a) Said of a crinoid having two circlets of plates proximal to the radial plates or (in some crinoids that lack radial plates) proximal to the oral plates. (b) Said of the apical system of an echinoid in which ocular and genital plates are arranged in two concentric circles, the genital plates alone in contact with the periproctal margin. Cf: monocyclic.