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SEP 



has plainly written in the book of 

 nature ; folly, past all excuse, to 

 suppose that the moral evidence of 

 an eternity of the future shall be 

 weakened by admitting the physical 

 evidence for an immensity of the 

 past." 



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. Sectile 

 minerals are those which are mid- 

 way between malleable and brittle. 

 "A slice or portion cut from a 

 sectile mineral is fragile, and the 

 new surface on the mass is smooth 

 and shining." Phillips. 



SECT/RIFORM. (from securis, a hatchet, 

 Lat. and form.) Hatchet-shaped : 

 a term applied to shells and to 

 leaves. 



SEDIMENTARY ROCKS. Rocks which 

 have been deposited by water. 



SEED VE'SSEL. In botany, the pericarp. 



SE'LENITE. ftffcXifvrnf*, Gr. selemte, 

 Pr.) Sulphate of lime, or crystal- 

 lized gypsum. A transparent and 

 highly crystallized variety of gyp- 

 sum. The crystals of selenite are 

 frequently united, or collected into 

 groups of various forms. Selenite 

 consists of lime 33-0, sulphuric 

 acid 44'8, water 21-0. It is found 

 abundantly in the gypsum and salt 

 formations. The primitive form of 

 its crystal is a dodecahedron, 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. 



SELE'NIUM. (from ffeXyvrj, the moon, 

 Gr.) One of the simple or ele- 

 mentary bodies, and a non-con- 

 ductor of electricity. According to 

 Prout, it appears to constitute the 



connecting link between sulphur 

 and the metals. When in mass, 

 selenium has the aspect of lead and 

 a metallic lustre, but pulverized it 

 displays a deep red colour. Speci- 

 fic gravity 4-3. Its equivalent is 

 39-6 : symbol Se. 



SE'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 to 2'5. It is infusible 

 before the blow-pipe. It consists 

 of silica 85, alumina 3, oxide of 

 iron 1'74, carbon 5, ammoniacal 

 water 8, with a fracture of bitu- 

 minous oil : or, according to 

 another analysis, of silica 82*7, 

 water 10, oxide of iron 3, alumina 

 3-5. 



SENSO'RIUM. (sensorium, Lat. sen- 

 sorium, Pr.) That part of the 

 brain where the senses transmit 

 the impressions or perceptions to 

 the mind. 



SE'PAL. This word 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. See Cuttle-fish. 



2. The ink of the cuttle-fish. This 

 has been found in a beautiful state 

 of preservation in fossil ink-bags of 

 sepiaB in the lias at Lyme Regis. 

 The common sepia used in drawing 

 is from the ink-bag of an oriental 

 species. 



SEPIOSTA'IRE. The name given by 

 Blainville to the internal bone of 

 the sepia or cuttle-fish. The ab- 

 sence of a siphuncle renders the 

 sepiostaire an organ of more simple 

 structure, and of lower office, than 

 the more compound shell of the 

 belemnite. 



SEPTA'RIA. (from septa, partitions, 

 Lat.) Spheroidal concretions, va- 



