GAS 



GEM 



GA'NGUE. A term applied to the 

 stones found in the cavities which form 

 the veins of metals, constituting the ma- 

 trix of the ore. 



GA'NOID FISHES (701/09, splendour, 

 elaop, likeness). A group of fossil fishes, 

 found in the old red sandstone, and other 

 rocks of that period, and named from the 

 brilliant lustte of their scales, which are 

 generally coated with polished enamel. 

 See Placoid Fishes. 



GAPING. A term applied to a bivalve 

 shell, when any parts of the margins do 

 not meet each other. 



GARNET. A simple mineral, gene- 

 rally of a deep red colour, crystallized ; 

 occurring most frequently in mica slate, 

 but also in granite and other igneous 

 rocks. Common garnet is less hard, and 

 less transparent than Precious Garnet, 

 which is often perfectly diaphanous. 

 Resinous garnet is another name for the 

 mineral colophonite. 



GARNET-BLENDE. Zinc-blende. A 

 sulphuret of zinc ; a massive mineral of 

 adamantine lustre, and often black. 



GAS. An old Teutonic word, signifying 

 air or spirit ; now applied to permanent 

 aeriform fluids for the purpose of distin- 

 guishing them from common air, which 

 is a mixture of two kinds of gas. Gases 

 are distinguished from liquids by the 

 name of elastic fluids ; and from vapours, 

 by their retaining their elasticity in all 

 temperatures. 



GASO'METER. A gas-holder ; a me- 

 tallic apparatus for containing a large 

 quantity of any gas which is insoluble 

 in water. 



GASTERO'PODA (yao-rJ/p, the sto- 

 mach, 7r63ey, feet). The third class of 

 the Mollusca, including the slugs and 

 shell-snails, and distinguished by the 

 structure and position of their locomo- 

 tive apparatus, which consists of a mus- 

 cular disc attached to the ventral surface 

 of the body, serving either as an instru- 

 ment for crawling, or, in rarer instances, 

 compressed into a muscular membrane 

 for swimming. They may be divided 

 into three orders by the forms of their 

 respiratory organs and of their external 

 covering : — 



1. Nudibranchia, or those which 

 breathe by branchiae unprotected by an 

 external or internal shell. 



2. Tectibranchia, or those which have 

 the branchiae protected by an external 

 or mternal calcareous covering. 



3. Pulmonata, or those which respire 

 by means of a pulmonary sac. 



148 



GAY-LUSSITE. A crystalline mine- 

 ral found abundantly in South America, 

 and named from the French chemist Gay 

 Lussac, who ascertained it to be a double 

 carbonate of soda and lime, with 5 equi- 

 valents of water. 



GECKO'TIDiE. The Gecko tribe; a 

 natural family of Saurians, named from 

 the genus gecko, and characterized by the 

 peculiar structure of the foot, the sole of 

 which is converted into a sucker, enabling 

 the animal to crawl up walls and along 

 ceilings, after the manner of the flies on 

 which they feed. 



GE'HLENITE. A mineral, allied to 

 Vesuvian, found together with calcareous 

 spar in the valley of Fassa in the Tyrol. 



GE'INE (7J7tVop, earthy). Geic acid. 

 Another name for humus, or vegetable 

 mould, produced by the decomposition of 

 vegetable matters. 



GE'LATINE {gelu, frost). An animal 

 or vegetable substance, constituting the 

 principle of jelly, and distinguished from 

 albumen by its not becoming consistent 

 by heat. The purest variety of gelatine 

 is isinglass; the common gelatine of 

 commerce is glue; and the hydrate of 

 gelatine is jelly. 



GE'LATINES. The term applied by 

 Mr. Kirby to the Acalephce of Cuvier, or 

 the Radiaires molasses of Lamarck, from 

 the gelatinous consistency of their bodies. 



GE'MINI. The third of the zodiacal 

 constellations, consisting of eighty-five 

 stars, the principal of which are Castor 

 and Pollux. It denotes the third month 

 of Autumn, from the 20th of November 

 to the 20th of December. In the Egyp- 

 tian zodiac this sign is represented by a 

 young man and a girl. In this month 

 seeds germinate. The Greek appellation 

 for this sign, diSv/jLoi, is vague. 



GEMITRI'CES (gemo, to moan or 

 coo). Cooers ; an order of Birds, com- 

 prising, according to Macgillivray, the 

 single family of Columbince, or Pigeons, 

 and named from their peculiar cooing 

 sound. 



GE'MMA. A leaf-bud, or the rudi- 

 ment of a young branch, consisting of 

 scales sviTTOundmga,growitig point, which 

 is in direct communication with the 

 woody and cellular tissue of the stem. 

 This term, as applied to zoophytes, de- 

 notes a young animal not enclosed in an 

 envelope or egg. 



GEMMA, a CORONA BOREALIS. 

 Alphacea. A star of the second magni- 

 tude in the Northern Crown. 



GEMMI'PAROUS {gemma, a bud, 



