SHE 



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S I L 



species. Buckland. DeLaBeche. Lyell. 

 Thomsom. Brown. Brewster. 



SHELL MARL. A deposite of calcareous 

 earth and clay containing shells. 



SHI'NGLE. (schindel, Germ.) The loose, 

 water-worn, pebbles on the sea-shore. 



SHIST. See Schist. 



SHO'OTING STARS. Shooting stars and me- 

 teors differ from aerolites in several re- 

 spects. They burst from the clear azure 

 sky, and darting along the heavens are 

 extinguished without leaving any resi- 

 duum, except a vapour-like smoke, and 

 generally without noise. Their parallax 

 shows them to be very high in the atmo- 

 sphere, sometimes even beyond its sup- 

 posed limit, and the direction of their 

 motion is, for the most part diametrically 

 opposite to the motion of the earth in its 

 planet. The astonishing multitudes of 

 shooting stars that have appeared within 

 these few years at stated periods, over the 

 American continent, and other parts of 

 the globe, warrant the conclusion that 

 there is either a nebula, or that there are 

 myriads of bodies revolving in groups 

 around the sun, which only become visi- 

 ble when inflamed by entering our at- 

 mosphere. 



SHORL. See Schorl. 



SHO'RLITE. See Schorlite. 



SIBE'RITE. Another name for Rubellite, 

 or red tourmaline. 



SI'DERO-CA'LCITE. The name given by 

 Kirwan to brown spar ; the braun spath 

 of Werner. 



SIDE'RUM. The name given by Bergman, 

 who took it for a new metal, to phosphu- 

 ret of iron. 



SI'ENITE. ) (from Siena, a city of Egypt, 



SY'ENITE. $ where this rock occurs in 

 abundance, and whence the Romans ob- 

 tained it for architectural and other pur- 

 poses.) Werner gave the name of 

 sienite to aggregates composed of felspar, 

 hornblende, and quartz ; or of felspar, 

 hornblende, quartz, and mica. Sienite is 

 the roche feldspathique of Haiiy. It often 

 bears the general aspect of a granite. 

 Felspar and hornblende may be deemed 

 its two constant and essential ingredients, 

 but it frequently contains quartz and 

 mica, and occasionally talc and epidote. 

 It is the presence of hornblende, as a 

 constituent part, which distinguishes this 

 rock from certain granites, that acci- 

 dentally contain hornblende. The struc- 

 ture of sienite is commonly granular ; 

 but the grains are sometimes coarse, and 

 sometimes very fine. In some instances 

 the structure of sienite is slaty. Green- 

 stone and sienite are essentially composed 

 of the same ingredients, namely, felspar 

 and hornblende ; from granitic green- 

 stone there is a transition to sienite, and 



from sienite to true granite. The colour 

 of sienite is usually grey, but this is 

 affected by the ingredients entering into 

 its composition. Cleaveland. 



SIENI'TIC. Containing sienite ; resembling 

 sienite ; possessing some of the characters 

 of sienite. Sienitic granite contains 

 hornblende. Sienitic porphyry is fine- 

 grained sienite containing large crystals 

 of felspar. 



SIGARE'TUS. A genus of marine univalve 

 shells belonging to the family Macrosto- 

 mata. It is a depressed, oval, nearly 

 auriform shell, with a short spiral colu- 

 mella : the aperture entire, wide, spread 

 out towards the summit of the right lip, 

 and longer than wide. It is a Tuscan 

 fossil, and exceedingly rare. The living 

 sigaretus is found in sand at depths vary- 

 ing from five to fifteen fathoms. 



SIGILLA'RIA. (from sigillum, Lat.) The 

 name given by M. Ad. Brongniart, to- 

 certain large, and, in modern vegetation, 

 unknown forms of plants discovered in 

 the coal formation : the name has been 

 assigned from the peculiar impressions 

 on the stems. The stems are of various 

 sizes from a few inches to upwards of 

 three feet in circumference, and of great 

 length. They are scattered throughout 

 the sandstones and shales that accompany 

 the coal, and may occasionally be seen in 

 the coal itself. These stems are inclined 

 in all directions, and some of them are 

 nearly vertical : they are supposed to 

 have been hollow, like the reed, and with 

 but little substance. M. Ad. Brongniart 

 has enumerated nearly fifty species. 



SI'LEX. (silex, Lat. flint.) An oxide of 

 silicon, constituting the greater part of 

 all the rocks of which the crust of the 

 earth is composed. 



SI'LICA. The same as silex. One hundred 

 parts of silica contain 48-4 of silicium, and 

 51*6 of oxygen. It is white ; its specific 

 gravity is 2*6 ; it is fusible. 



SILICICA'LCE, The quartz agathe calcifere 

 of Haiiy : silex silicicalce of Brongniart. 

 A substance occurring in amorphous 

 masses, in thin beds, under strata of 

 compact limestone, in Provence. It is of 

 a grey or brown colour, sometimes nearly 

 black. It effervesces with nitric acid ; 

 and before the blow-pipe fuses into a 

 white scoria. It is a mixture of flint and 

 carbonate of lime. 



SILI'CEOUS. Containing silex ; flinty ; 

 having the appearance or properties of 

 flint. Thus we have siliceous limestone ; 

 siliceous slate ; siliceous nodules, &c. 



SILI'CIFY. To convert into flint ; to petrify. 



SILICIFICA'TION. Called also petrifaction. 

 The conversion of any substance into 

 stone by the infiltration of siliceous 

 matter. 



