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xisted, including the Silurian, Devonian, and Carboniferous ages, and also to the life or rocks of those ages. See Chart of Geology.

Having a completely idiomorphic structure; -- said of certain rocks.

A genus of large arenaceous fossil Foraminifera found in the Cretaceous rocks. The species are globular, or nearly so, and are of all sizes up to that of a tennis ball.

A glassy volcanic rock of a grayish color and pearly luster, often having a spherulitic concretionary structure due to the curved cracks produced by contraction in cooling. See Illust. under Perlitic.

Transparent and colorless rock crystal; as, Brazilian pebble; -- so called by opticians. Pebble powder, slow-burning gunpowder, in large cubical grains. -- Scotch pebble, varieties of quartz, as agate, chalcedony, etc., obtained from cavities in amygdaloid.

More generally, a coarse granite occurring as vein material in other rocks.

Of, pertaining to, or resembling, pegmatite; as, the pegmatic structure of certain rocks resembling graphic granite.

us or other instrument for scratching or graving. Graven with an iron pen and lead in the rock. Job xix. 24.

Jutting over; projecting; overhanging. "A vapor sometime like a . . . pendent rock." Shak.

A volcanic rock, formed by the cementing together of sand, scoria, cinders, etc.

An eruptive rock characterized by the presence of chrysolite (peridot). It also usually contains pyroxene, enstatite, chromite, etc. It is often altered to serpentine.

Relating to or resembling perlite, or pearlstone; as, the perlitic structure of certain rocks. See Pearlite.

Of or pertaining to to rock. G. S. Faber.

A combining form from Gr. rock, stone; as, petrology, petroglyphic.

Any Australian kangaroo of the genus Petrogale, as the rock wallaby (P. penicillata).

The art or operation of carving figures or inscriptions on rock or stone.

The scientific description of rocks; that department of science which investigates the constitution of rocks; petrology.

Rock oil, mineral oil, or natural oil, a dark brown or greenish inflammable liquid, which, at certain points, exists in the upper strata of the earth, from whence it is pumped, or forced by pressure of the gas attending it. It consists of a complex mixture of various hydrocarbons, largely of the methane series, but may…

partment of science which is concerned with the mineralogical and chemical composition of rocks, and with their classification: lithology.

Like stone; hard; stony; rocky; as, the petrous part of the temporal bone. Hooper.