DIKE, or DYKE (AS. die, Icel. dik, AMC. lick Ger. Teich, pool; probably connected ulti mately with Gk. rdxos, teichos, wall). In geol ogy, a relatively thin body of igneous rock occur ring between the separated walls of a fissure. It differs from vein, which it resembles in form, in having originated by the intrusion and con solidation of molten material, and not by the deposition of minerals from solution. Dikes are usually inclined at considerable angles from the horizontal, and, when the adjacent rock has de cayed, they project above the surface like walls of masonry. They vary in width from a few inches to hundreds of feet, the larger dikes some times extending a distance of many miles: they reach downward to unknown depths. Proof of their igneous origin is found in the great changes which the strata forming their walls have suf fered by the intense beat. Limestone in contact with dikes is changed to crystalline marble: shale is hardened to slate, or by the development of new minerals becomes sehist ; and bituminous coal assumes the character of anthravite. While
of wide occurrence, dikes are especially frequent in regions of crustal folding and volcanic lis th•bauie. ThPy are often found traversing the sides of volcanoes, where they originate during eruptions by fissuring of the colic and filling of the cracks with lava. The consolidation of igne ous rocks in the form of dikes develops peculiar of structure, and this fact has been used by some authorities as the basis of a rock class known as 'dike rocks.' See GEOLOGY: 1cxcous ItocK!-;: VoLcAxo.
DIKE. of earth. most com monly one used to reclaim or protect sub ject to flooding or formed in land drainage opera I he term is applied to low (atilt generally such a, are auxiliary to the main dam. forming an artificial reservoir by closing minor outlets from the natural basin. see DANts; DuAINAi,E; 1.1AEt:s.