SEC 



[232 ] 



S E 11 



dence for an immensity of the past." 

 Phillips. Buckland. Mantell. Bake- 

 well. 



SE'CTILE. (from sectilis, that may be easily 

 cut, Lat.) A term in mineralogy, applied 

 to minerals, when, being cut with a knife, 

 the separated particles do not fly away, 

 but remain on the mass. 



SE'CULAR REFRJGERA'TION. The periodi- 

 cal cooling and consolidation of the globe 

 from a supposed original state of fluidity 

 from heat. LyelVs Principles of Geology. 



SECU'RIFORM. (from securis, a hatchet, 

 Lat. and form.} Hatchet-shaped : a term 

 applied to shells and to leaves. 



SE'DIMENT. (sedimentum, Lat. sediment, 

 Fr.) That which subsides, or settles at 

 the bottom. 



SEDIMENTARY ROCKS. Rocks which have 

 been deposited by water. 



SEED VE'SSEL. In botany, the pericarp. 



SE'J.ENITE. (o-tXj/rtTT/g, Gr. selenite, Fr.) 

 Sulphate of lime, or crystallized gypsum. 

 A transparent and highly crystallized va- 

 riety of gypsum. The crystals of selenite 

 are frequently united, or collected into 

 groups of various forms. Selenite con- 

 sists of lime 33-0, sulphuric acid 44-8, 

 water 21 '0. It is found abundantly in 

 the gypsum and salt formations of Eng- 

 land, France, Germany, &c., &c. The 

 primitive form of its crystals is a dodeca- 

 hedron, which may be conceived as two 

 four- sided pyramids, applied base to base, 

 and which, instead of terminating in 

 pointed summits, are truncated near the 

 bases ; so that the sides of the pyramids 

 are trapeziums, each terminating in a 

 rhomb. It causes double refraction. 

 Before the blow-pipe it melts into a white 

 enamel. It does not effervesce with mu- 

 riatic acid, unless it be impure. 



SELE'NIUM. (from GtXrjvrj, the moon, Gr.) 

 One of the fifty-five simple or elementary 

 bodies, and a non-conductor of electricity. 

 It was extracted by Berzelius from the 

 pyrites of Fahlun. According to Dr. 

 Prout, it appears to constitute the con- 

 necting link between sulphur and the 

 metals. 



SELF-LU'M INDUS BO'DIES. All visible bo- 

 dies may be divided into self-luminous 

 and non-luminous. Self-luminous bodies, 

 such as the stars, flames of all kinds, and 

 bodies which shine by being heated or 

 rubbed, are those which possess in them- 

 selves the property of discharging light. 

 Dr. Brewster. 



SE'MI. (semi, Lat.) In composition with 

 other words, implies half; as semi-sphe- 

 rical ; semi-transparent, &c. , &c. 



SE'MINAL LEAVES. The first leaves of a 

 plant. 



SB'MI-O'PAL. A variety of opal. The 

 Halbopal of Werner ; La demi-opale of 



Brochant ; Quartz resinite commune of 

 Haiiy. The colours of semi-opal are 

 white, grey, green, red, brown, and blue. 

 Fracture imperfectly conchoidal. Specific 

 gravity 2'0 to 2 P 5. It is infusible before 

 the blow-pipe. It consists of silica 85 - 0, 

 alumina 3*0, oxide of iron T74, carbon 

 5-0, amrnoniacal water 8-0, with a fraction 

 of bituminous oil : or, according to an- 

 other analysis, of silica 82'7, water lO'O, 

 oxide of iron 3'0, alumina 3'5. 



SENSO'RIUM. (sensorium, Lat. sensorium, 

 Fr.) That particular part of the brain 

 in which sensation produces percep- 

 tion. 



SE'PAL. This word has no derivation, but 

 was invented by botanists to distinguish 

 the several parts of the calyx from those 

 of the corolla. 



SE'PIA. 



1. The name given by Linnaeus to the 

 cuttle-fish. A genus of cephalopods com- 

 prising several subgenera, the two most 

 interesting of which are the Argonauta of 

 Linnaeus and the Sepia of Lamarck. For 

 a description of sepia the reader is referred 

 to the article Cuttle-fish. 



2. The ink of the cuttle-fish. This has 

 been found in a beautiful state of pre- 

 servation in fossil ink -bags of sepise in the 

 lias at Lyme Regis. The common sepia, 

 used in drawing, is from the ink-bag of an 

 oriental species of cuttle-fish. 



SE'PIOSTAIRE. The name given, by Blain- 

 ville, to the internal bone of the sepia or 

 cuttle-fish. The absence of a siphuncle 

 renders the sepiostaire an organ of more 

 simple structure, and of lower office, than 

 the more compound shell of the belem- 

 nite. 



SEPTA'RIA. (from septa, inclosures, Lat ) 

 Spheroidal concretions, varying from a 

 few inches to a foot in diameter, and 

 divided into cells or chambers of irregular 

 form ; sometimes they are nodules of 

 clay, having the chambers filled with 

 spar ; they are usually found in argilla- 

 ceous strata. Masses of argillaceous 

 limestone, traversed interiorly by cracks 

 passing in different directions, and con- 

 taining calcareous spar. 



SE'PTUM. (septum, Lat.) A partition. 

 The plates dividing the chambers of mul- 

 tilocular shells are termed septa ; a par- 

 tition separating certain portions of the 

 brain is called the septum ; and the car- 

 tilaginous partition of the nostrils is called 

 the septum of the nose. 



SE'ROLIS. A genus of crustaceans, afford- 

 ing the nearest approach among living 

 animals to the external form of the trilo- 

 bite. This genus was first established by 

 Dr. Leach. The greatest difference be- 

 tween the serolis and trilobite consists in 

 the former possessing a fully developed 



