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The laying bare of rocks by the washing away of the overlying earth, etc.; or the excavation and removal of them by the action of running water.

Of secondary origin; -- said of certain rocks whose material has been derived from older rocks.

Of or pertaining to Devon or Devonshire in England; as, the Devonian rocks, period, or system. Devonian age (Geol.), the age next older than the Carboniferous and later than the Silurian; -- called also the Age of fishes. The various strata of this age compose the Devonian formation or system, and include the old red s…

A basic, dark-colored, holocrystalline, igneous rock, consisting essentially of a triclinic feldspar and pyroxene with magnetic iron; -- often limited to rocks pretertiary in age. It includes part of what was early called greenstone.

A dark green or bronze-colored laminated variety of pyroxene, common in certain igneous rocks.

he center of an object from side to side; width; thickness; as, the diameter of a tree or rock.

A wall-like mass of mineral matter, usually an intrusion of igneous rocks, filling up rents or fissures in the original strata.

To incline downward from the plane of the horizon; as, strata of rock dip.

pear; to bring to light; to reveal. How softly on the Spanish shore she plays, Disclosing rock, and slope, and forest brown! Byron. Her lively looks a sprightly mind disclose. Pope.

parts; to reduce to fragments or to powder; to break up, or cause to fall to pieces, as a rock, by blows of a hammer, frost, rain, and other mechanical or atmospheric influences. Marlites are not disintegrated by exposure to the atmosphere, at least in six years. Kirwan.

The displacement of parts of rocks or portions of strata from the situation which they originally occupied. Slips, faults, and the like, are dislocations.

t asunder or broken in pieces; breach; rent; dilaceration; rupture; as, the disruption of rocks in an earthquake; disruption of a state.

An igneous rock composed of orthoclase, elæolite, and sodalite.

; a divisional surgeon of police. Divisional planes (Geol.), planes of separation between rock masses. They include joints.

A sort of stone, found in the mines with the true alum rock, chiefly of silica and iron.

A dark-colored, basic, igneous rock, composed essentially of pyroxene and a triclinic feldspar with magnetic iron. By many authors it is considered equivalent to a coarse-grained basalt.

The sudden drop or depression of the strata of rocks on one side of a fault. See Throw, n.

A coat with skirts behind only, as distinct from the frock coat, of which the skirts surround the body. It is worn on occasions of ceremony. The dress coat of officers of the United States army is a full-skirted frock coat.

A collection of loose earth and rocks, or boulders, which have been distributed over large portions of the earth's surface, especially in latitudes north of forty degrees, by the agency of ice.

pierce or bore with a drill, or a with a drill; to perforate; as, to drill a hole into a rock; to drill a piece of metal.