ives its name from having a coarse _granular_
structure; _granum_, Latin for grain. Waterloo bridge, and the
paving-stones in the carriage-way of the London streets, afford good
examples of the most common varieties of granite.

GREENSAND. Beds of sand, sandstone, limestone, belonging to the
Cretaceous Period. The name is given to these beds because they
often, but not always, contain an abundance of green earth or
chlorite scattered through the substance of the sandstone,
limestone, &c.

GREENSTONE. A variety of trap, composed of hornblende and felspar.

GREYWACKE. _Grauwacke_, a German name, generally adopted by
geologists for some of the most ancient fossiliferous strata. The
rock is very often of a gray color; hence the name, _grau_, being
German for gray, and _wacke_, being a provincial miner's term.

GRIT. A provincial name for a coarse-grained sandstone.

GYMNOSPERMOUS. _Etym._, [Greek: gymnos], _gymnos_, naked, and
[Greek: sperma], _sperma_, a seed. (See GYMNOGENS.)

GYMNOGENS. A class of flowering plants, in which the ovules are not
inclosed in an ovary. They are also called _gymnosperms_, the seeds
in like manner not being inclosed in a pericarp. It includes all
_Coniferae_, as pine, fir, juniper, cypress, yew, cedar, &c., and
_Cycadeae_. All are Dicotyledonous (a few have many cotyledons), and
all Exogenous, except _Cycas_, the growth of which is anomalous. The
term is applied in contradistinction to _Angiosperms_, which see.
_Etym._, [Greek: gymnos], naked, and [Greek: genesis], increase.

GYPSUM. A mineral composed of lime and sulphuric acid, hence called
also _sulphate_ of _lime_. Plaster and stucco are obtained by
exposing gypsum to a strong heat. It is found so abundantly near
Paris, that plaster of Paris is a common term in this country for
the white powder of which casts are made. The term is used by Pliny
for a stone used for the same purposes by the ancients. The
derivation is unknown.

GYPSEOUS, of or belonging to gypsum.

GYROGONITES. Bodies found in freshwater deposits, originally
supposed to be microscopic shells, but subsequently discovered to be
seed-vessels of freshwater plants of the genus _Chara_. See above
p. 742. _Etym._, [Greek: gyros], _gyros_, curved, and [Greek:
gonos], _gonos_, seed, on account of their external structure.

HEMIPTERA. An order of