G L A 



[ 10!) ] 



G R E 



crystalline. According to the Huttonian 

 theory, the materials composing gneiss 

 were originally deposited from water ; but 

 from the influence of subterranean heat, 

 became altered so as to assume a new 

 texture. The structure of gneiss is always 

 more or less distinctly slaty, when viewed 

 in the mass ; although individual layers 

 may possess a granular structure. When 

 this mineral is broken perpendicularly to 

 the direction of its strata, its fracture has 

 commonly a striped aspect. This rock, 

 though slaty in its structure, is rarely 

 perfectly fissile. Gneiss, like granite, 

 never contains any fossil remains ; when 

 it occurs with granite, it usually lies im- 

 mediately over the granite j or, if the 

 strata be highly inclined, it appears rather 

 to rest against the granite than to be 

 incumbent upon it. Gneiss is more or 

 less distinctly stratified, and the strata 

 are often inclined to the horizon at a 

 very great angle ; indeed, they are some- 

 times nearly, or quite, vertical. Moun- 

 tains composed of gneiss are seldom so 

 steep as those of granite, and their sum~ 

 mits, instead of presenting those needle- 

 like points, or aiguilles, which charac- 

 terize granitic mountains, are usually 

 rounded. Few of the primary rocks are 

 so metalliferous as gneiss. Its ores oc- 

 cur both in beds and veins : more fre- 

 quently in the latter. 



GLA'NDULOUS GNEISS. A variety of gneiss, 

 (in which the mica is sometimes ar- 

 ranged in undulated layers,) presenting 

 numerous small masses of felspar or 

 quartz, of a globular or ellipitical form, 

 interspersed like glands through the 

 mass. From this circumstance it has 

 obtained its name. 



GOLD. (Sax.) A metal, when pure, of a 

 rich yellow colour : specific gravity 19 '3. 

 It does not readily combine with oxygen ; 

 hence it does not rust when exposed to 

 the air, and it may be melted and re- 

 melted frequently with scarcely any dimi- 

 nution of its quantity. It is said to have 

 been kept in a state of fusion for nearly 

 eight months without undergoing any 

 perceptible change. In ductility and 

 malleability it surpasses all other metals, 

 and it may be beaten into leaves so ex- 

 ceedingly thin, that one grain of gold 

 shall cover fifty-six square inches, such 

 leaves having the thickness only of one 

 282,000th part of an inch. Its tenacity 

 is inferior to that of iron, copper, pla- 

 tinum, and silver. Gold is soluble in 

 nitro-muriatic acid, and in a solution of 

 chlorine. The gold coins of this country 

 contain one-twelfth part of copper alloy : 

 jewellers' gold is a mixture of gold and 

 copper in the proportions of three-fourths 

 of pure gold and one-fourth of copper. 



GOLT. See Gault, 



GONI'ATITES. A sub-genus of ammonites, 

 in which the last whorl covers the spire. 

 Seven species have been found in the 

 carboniferous system, and seventeen in 

 the primary strata. 



GONIO'METER. (from yom'a, an angle, 

 and fjLkrpov, a measure, Gr.) An instru- 

 ment invented by M. Carangeau, for the 

 accurate measurement of crystals. Dr. 

 Wollaston also invented a goniometer. 



GONYLE'PTES. A genus of the second order 

 of Pseudarachnidans, the posterior legs 

 exhibiting a raptorious character. 



GORGO'NIA. A genus of Ceratophyta, of 

 the family Corticati, class Polypi. These 

 animals have a horny skeleton, are car- 

 nivorous, feeding upon living animalcules. 

 The polypi of several species have been 

 observed, and they are found to possess 

 eight denticulated arms, a stomach, &c. 



GRA'LL^E. An order of aquatic birds. Wa- 

 ders ; frequenting marshes and streams ; 

 having long naked legs ; long neck ; 

 cylindrical bills. In this order are in- 

 cluded the crane, stork, heron, bittern, 

 &c. &c. 



GRA'MINA. (gramen, Lat.) The fourth 

 order in Linnseus's division ; the grasses. 



GRAMINEOUS. (gramineus,~Lat.) Grassy; 

 resembling grass. Gramineous plants are 

 such as have a long narrow leaf, and no 

 foot-stalk. 



GRAMINIVOROUS, (from gramen, grass, 

 and voro, to devour, Lat.) Subsisting 

 wholly on grass or vegetable food. Ani- 

 mals which subsist wholly on vegetable 

 food are called graminivorous, while those 

 which live on flesh alone are called car- 

 nivorous ; those feeding on both are 

 called omnivorous ; while those feeding 

 solely on fishes are denominated pisci- 

 vorous. 



GRA'MMATITE. (The name given by 

 Brongniart to Tremolin.) A mineral, a 

 variety of hornblende, confined almost 

 entirely to primary rocks. Colours white 

 and blue. Disposed in fibrous, radiated, 

 and granular concretions. 



GRA'NATINE. A name given by Mr. Kir- 

 wan to a granular aggregate containing 

 three ingredients, but those differing from 

 the ingredients of granite. A compound 

 embracing two ingredients only, he 

 termed agranitell; when three ingredi- 

 ents are present, but not the three form- 

 ing granite, he called it a granatine ; 

 when more than three ingredients form 

 the compound, he termed it a granilite. 



GRA'NATITE. > The Prismatoidischer gra- 



GRE'NATITE. $ nat of Mohs, Granatit of 

 Werner, Staurotide of Haiiy. A reddish- 

 brown mineral, occurring in primary 

 rocks in the Shetland Isles, and in many 

 parts of Scotland, and in America. Ac- 



