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Show 80 GLOSSARY materials having been thrown down from a state of suspension or solution in water. SELENITE. Crystallized gypsum, or sulphate of lime..-a simple mineral. SEPTA RIA. Flattened balls of stone, generally a kind of iron-stone, which, on being split, are seen to be separated in their interior into irregular masses. Elym., septa, inclosures. SERPENTINE. A rock usually containing much magnesian earth, for the most part unstratified, but sometimes appearing to be an altered or metamorphic stratified rock Its name is derived from frequently presenting contrasts of colour, like the skin of some serpents. SHALE. A provincial term, adopted in geological science, to express an indurated slaty clay. Etym., German schalen, to peal, to split. SHELL MARL. A deposit of clay, peat, and other substances mixe<l with shells, which collects at the bottom of lakes. SHINGLE. The loose and completely water-worn gravel on the seashore. SILEX. The name of one of the pure earths, being the Latin word for flint, which is wholly composed of that earth. ~rench geolorrists have applied it as a generic name for all mmerals comp: Secl entirely of that earth, of which there are many of different external forms. SILICA. One of the pure earths. Etym., silex, flint, because found in that mineral. SILICATE. A chemical compound of silica and another substance, such as silicate of iron. Consult elementary works on che-mistry. . . . SILICEous. Of or belonging to the earth of flmt. Etym., s1lex, wh1eh see. A siliceous rock is one mainly composed of silex. SILICIFIED. Any substance that is petrified or mineralized by siliceous earth. SILT. The more comminuted sand, clay, and earth, which is transported by running water. It is often accumulated by currents in banks. Thus we speak of the mouth of a river being silted up when its entrance into the sea is impeded by such accumulation of loose materials. SIMPLE MINERAL. Individual mineral substances, as distinguished from rocks, which last are usually an aggregation of simple minerals. They are not simple in regard to their nature, f?r when subjected to chemical analysis, they are ~ound. to cons.tst of. a variety of different substances. Pyrites 1s a simple mmeral m GLOSSARY. 81 tl1e sense we use the t b erm, ut it is a chernical compound of sulphur and iron. SoLPATARA. A volca · f . ntc vent rom wInch sulphur sulphureous watery ' and aCI' d vapours and gases are emitted. ' ' SPORULES .. T~e reproductory corpuscula (minute bodies) of cryp .. togamic pains. Etym., o"rropa, spora, a seed. STALACTITE. When water holding lime in solution deposits it as it drop!:! from the roof of 1 . . . a cavern, ong rods of stone hang down ltke Icicles, and these are called stalactites Ely ' ,. sta l azo, to drop. . m., O'Ta"a.,w ' SuLAGMITE. When water holding lime in solution drops on the floor of a cavern, the water evaporating leaves a crust composed of layers of limestone ; such a crust is called stalagmite, fro~ O'ra>..ay,_,.a, stalagma, a drop, in opposition to stalactite whJCh see. ' STILBIT~. A white c?stallized simple mineral, one of the Zeolite family, frequently mcluded in the mass of the trap rocks. STRATIFIED. Rocks arranged in the form of strata, which see. STRATIFICATION. An arrangement of rocks in strata, which see. SrRA'fUl\I, STRATA. When several rocks lie like the leaves of a book one upon another, each individual forms a stratum ;-strata i~ the plural of the word. Etym., stratum part of a Latin verb signifying to strew or lay out. ' STRIKE .. The direction or line of bearing of strata, which is always at right angles to their prevailing dip. For a fuller explana· tion, see val. iii. p. 346. SunAPE~NINEs. Low .hills.which skirt or lie at the foot of the great cham o.f the Apennm~s m Italy. The term Subapennine is applied geologJCally to a senes of strata of the Older Pliocene period. SYENITE. ~ kind of granite, so called because it was brought from Syene m Egypt. For geological acceptation of the term, see vol. iii. p. 358. SYNCLINAL Axis. See explanation of this term, vol. iii. p. 293. TALUS. "When fragments are broken off by the action of the weather from the face of a steep rock, as they accumulate at its foot, they form a sloping heap, called a talus. The term is borrowed from the language of fortification, where talus means the outside of a wall of which the thickness is diminished by degrees, as it rises in height, to make it the firmer. TARSI. The feet in insects, which are articulated, and formed of five or a less number of joints. TEn'riARY STRATA. A series of sedimentary rocks, with characters VoL,lll. f |