G R A 







G R A 



Lat.) Eating grain ; subsisting on 

 grain. 



GRA'NULAR. } Bodies containing, or com- 



GRA'NULARY. J posed of, small grains. 



GRA'NULAR LIMESTONE. A subspecies of 

 carbonate of lime, the result of a con- 

 fused or irregular crystallization. Struc- 

 ture foliated and granular. The grains 

 are of various sizes, from coarse to very 

 fine, sometimes, indeed, so fine that the 

 mass appears almost compact. W 7 hen 

 these grains are white and of a moderate 

 size, this mineral strongly resembles 

 white sugar in solid masses. Its fracture 

 is foliated, and when the structure is very 

 finely granular, the fracture often be- 

 comes a little splintery. It is more or 

 less translucent, but in the dark-coloured 

 varieties, at the edges only. Its colour 

 is most commonly white or gray, often 

 snow-white, and sometimes grayish black. 

 Some varieties are flexible when sawn into 

 thin slabs. Granular limestone is some- 

 times a pure carbonate of lime. It occurs 

 in very large masses, and is almost exclu- 

 sively found in primary rocks ; some- 

 times it occurs among secondary, but 

 then its relative age is easily determined 

 by the shells it contains, or the accom- 

 panying minerals. In the Pyrennees 

 vertical beds of granular limestone alter- 

 nate with granite, and trap, or the limestone 

 is sometimes intermixed with those rocks. 

 There are few countries in which gra- 

 nular limestone is not found. Italy and 

 Greece furnished the ancients with valu- 

 able quarries. Both granular and com- 

 pact limestone furnish numerous varieties 

 of marbles, but those which belong to 

 the former exhibit a more uniform colour, 

 are generally susceptible of a higher po- 

 lish, and are consequently most esteemed 

 for statuary and some other purposes. 

 Cleaveland. 



GRA'NULATE. (granuler, Fr.) To be 

 formed into small grains. 



GRA'NULATED. Having a structure resem- 

 bling grains ; formed into grains ; bead- 

 ed ; having small roundish elevations, 

 placed in rows. 



GRANULA'TION. (granulation, Fr.) 



1. The operation by which metals are 

 reduced into small grains. 



2. The act of forming into bodies resem- 

 bling aggregates of grains. 



GRA'NULE. (diminutive of grain.) A small 

 grain. 



GRA'NULOUS. Composed of grains; full of 

 small grains. 



GRA'PHIC GRA'NITE. A variety of granite, 

 composed of felspar and quartz, so ar- 

 ranged as to produce an imperfect laminar 

 structure. When a section of graphic 

 granite is made at right angles to the alter- 

 nations of the constituent minerals, bro- 



ken lines, resembling Hebrew characters, 

 present themselves ; hence its derivation. 



GRA'PHITE. Another name for black-lead, 

 or plumbago ; carburet of iron. Graphite 

 is of a dark steel-gray, or nearly iron- 

 black. It leaves on paper a well defined, 

 shining trace, which has very nearly the 

 colour of the mass, and consists of minute 

 grains. It is perfectly opaque, easily 

 scraped by a knife, and soils the fingers. 

 It is a conductor of electricity, and when 

 rubbed on sealing-wax till a metallic trace 

 appears, communicates no electricity to 

 the wax. Specific gravity from 1'98 to 

 2-26. Constituent 'parts, carbon 92'0, 

 iron 8'0. Cleaveland. 



GRA'PTOLITE. A fossil zoophyte, found in 

 the Silurian shales. 



GRA'VEL. Fragments of stones and flints ; 

 small pebbles. 



GRAVITA'TION. (gravitation, Fr. gravita* 

 zione, It.) The difference between gra- 

 vity and the centrifugal force induced by 

 the velocity of rotation or revolution : the 

 force which causes substances to fall to 

 the surface of the earth, and which retains 

 the celestial bodies in their orbits ; its 

 intensity increases as the squares of the 

 distance decrease. 



GRA'VITY. (gravite, Fr. gravita, It.) The 

 reciprocal attraction of matter on matter. 

 The force of gravity is every where per- 

 pendicular to the surface, and in direct 

 proportion to the quantity of matter. 



GRA'YWACKE. ^ (from grauwacke, Germ. 



GRAU'WACKE. ! a compound of grau, 



GRAUWACKE'. \ grey, and wacke, a 



GRE'YWACKE. J provincial term used by 

 miners.) The name given to a group of 

 rocks, being the lowest members of the 

 secondary strata. Mr. Lyell comprises in 

 this group the Ludlow, Wenlock and 

 Dudley, Horderly and May Hill rocks, 

 the Builth and Llandeilo flags, and the 

 Longmynd rocks. The French have 

 changed the name grauwacJce for trau- 

 mate, a word as little euphonic as the 

 one repudiated. Mr. Bakewell observes, 

 " Graywacke, in its most common form, 

 may be described as a coarse slate con- 

 taining particles or fragments of other 

 rocks or minerals, varying in size from 

 two or more inches to the smallest grain." 

 When the imbedded particles become ex- 

 tremely minute, graywacke passes into 

 common slate. When the particles and 

 fragments are numerous, and the slate in 

 which they are cemented can scarcely be 

 perceived, graywacke becomes coarse 

 sandstone, or gritstone. When the frag- 

 ments are larger and angular, graywacke 

 might be described as a breccia with a 

 paste of slate. When the fragments are 

 rounded it might not improperly be called 

 an ancient conglomerate. The old red 



