S I L 



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S I M 



SILI'CIUM. iThe hitherto undecomposed 

 SILICON. ) base of silica or silex. Of 

 the metallic bases of the alkalies and 

 earths, silicium is the most abundant on 

 the surface of our planet, silica entering 

 so largely into the composition of both 

 chemical and mechanical rocks. Accord- 

 ing to a table of Mr. De La Beche's, 

 gneiss contains 71 per cent, of silica ; 

 mica slate 73 per cent. : talcose slate 78 ; 

 granite 74 ; basalt 59, &c. &c. In pure 

 quartz rock, silica would be the only in- 

 gredient. Flint, quartz or rock-crystal, 

 &c., are hydrates of silicon, or silex with 

 some water of crystallization. 

 SILI'CULA. (Lat. a little husk or pod.) 



In botany, a species of fruit. 

 SILI'CTJLOTJS. Having small pods or husks. 

 SI'LIGIUA. (Lat.) A pod ; a long seed 

 vessel of two valves, separated by a linear 

 receptacle, on whose edges the seeds are 

 ranged alternately. 



SILIQ,UA'RIA. A genus of marine univalves, 

 found both fossil and recent. It is a 

 tubular shell, spiral at its beginning, con- 

 tinued in an irregular form ; divided 

 laterally, through its whole length, by a 

 narrow slit, and formed into chambers by 

 entire septa. Recent siliquarise have been 

 found in sponges ; they may be distin- 

 guished from serpulse by the longitudinal 

 slit. Cuvier places the genus in the order 

 Tubulibranchiata. Fossil siliquarise occur 

 at Grignon. 



Si'LiauosE. } Bearing pods. A term ap- 

 SI'LICIUOUS. S plied to plants having that 

 sort of pericarp denominated a pod or 

 legume. 



SI'LLIMANITE. A dark grey or brown mi- 

 neral, composed of silica 42-6, alumina 

 54'1, oxide of iron 1/9, water 0'5, dis- 

 covered at Saybrook, in Connecticut, and 

 named after Prof. Silliman. 

 SILT. The deposit of running water ; mud. 

 SI'LVAN. The name given by Werner to 



the metal tellurium. 



SI'LVER. (silber, Ger.) One of the fifty -five 

 simple or elementary bodies, and included 

 in the subdivision termed metals. When 

 pure, it is nearly white. It is superior to 

 gold in lustre, and inferior to it in malle- 

 ability ; it is however so malleable that 

 it may be beaten into leaves not ex- 

 ceeding 100,000th of an inch in thick- 

 ness. It is very ductile, surpassing gold 

 in tenacity, but inferior to iron, copper, 

 and platinum. It may be drawn out into 

 wire of greater fineness than human hair. 

 It is harder than gold, but softer than 

 copper, and may be easily cut by a knife. 

 Its specific gravity is 10-47. Silver fuses 

 at a temperature of about 1,000 degrees 

 Fahr. It is not oxidated by exposure to 

 the atmosphere, but becomes tarnished 

 by sulphureous vapours. It is tasteless, 



and free from smell. It is soluble in 

 nitric acid. Silver for domestic purposes, 

 as well as that made into coin, is rendered 

 harder by an alloy of copper. The 

 standard silver of this country consists of 

 eleven ounces two pennyweights of pure 

 silver and eighteen pennyweights of cop- 

 per. Silver has been known from the 

 earliest ages. It is found native and in 

 ores of several kinds. The ores of silver 

 occur in metallic veins, traversing primary 

 rocks. There are many ores which yield 

 silver that are not, strictly speaking, ores 

 of silver. Although the mines of Europe 

 yield considerable quantities of silver, 

 yet it is to Mexico and Peru that we are 

 indebted for the main supplies. The 

 mines of Potosi have paid a royal duty 

 on silver valued at 234,700,000/. ster- 

 ling. 



SILU'RIAN. The name given by Mr. Mur- 

 chison to an upper subdivision of the 

 sedimentary strata found below the old 

 red sandstone. Mr. Murchison assigned 

 this name to these strata from their being 

 best developed in that portion of England 

 and Wales formerly included in the an- 

 cient British kingdom of the Silures. 

 The Silurian rocks are divided into up- 

 per and lower : the upper Silurian rocks 

 comprise the Ludlow formation and the 

 Wenlock formation ; the Ludlow forma- 

 tion consisting of the upper Ludlow rock, 

 the Aymestry limestone, and the lower 

 Ludlow rock ; the Wenlock formation 

 consisting of the Wenlock limestone and 

 the Wenlock shale : the lower Silurian 

 rocks are subdivided into the Caradoc 

 formation and the Llandeilo formation ; 

 the Caradoc formation consisting of flags, 

 sandstones, grits, and limestones ; the 

 Llandeilo formation, of calcareous, dark- 

 coloured flags, with sandstone and schist. 

 The whole of the Silurian rocks attain a 

 thickness in some parts of seven thou- 

 sand five hundred feet. They are all 

 marine deposites. Upwards of five hun- 

 dred and fifty species of organic beings 

 have been discovered in the Silurian 

 rocks. The name Greywacke has been 

 also given to this group. 



SI'MIA. (simia, an ape, Lat.) A genus of 

 Quadrumana. The ape. The lower jaw 

 of an ape has been discovered in the 

 miocene strata, in the department of 

 Gers, in France. 



SI'MPLE. (simplex, Lat. simple, Fr. sem- 

 plice, It.) 



1. In botany, applied to roots, when 

 undivided ; to a leaf, when consisting 

 of only one leaf, and not divided into 

 leaflets, &c. &c. 



2. In mineralogy, a term applied to ele- 

 mentary, or undecomposed substances : 

 these are fifty-five in number, and are 



