SIP 



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apparatus belonging to chambered 

 or polythalamous shells, passing 

 through the several chambers, and 

 terminating in a large sac, which 

 surrounds the heart of the animal. 

 The use of the siphunculus appears 

 to be the enabling the animal to 

 rise to the surface, or descend to 

 the bottom of the water, by in- 

 creasing its specific gravity. 



SIPHO'NIA. A genus of zoophytes, 

 species of which have been discov- 

 ered in the chalk and in the green- 

 sand. One species also has been 

 found in the oolite. "A fossil 

 animal, with a polymorphous body, 

 supported by a stem proceeding 

 from a fusiform or ramose root- 

 like pedicle ; the original substance 

 spongeous, and pierced by a bundle 

 of tubes derived from the pedicle, 

 passing through the stem, then 

 ramifying and terminating on the 

 surface of the body." Parkinson. 



SI'PHTJNCLED. Possessing a siphuncle ; 

 formed with a siphuncle. 



SI'TU. (situs, Lat.) " In situ " is a 

 term used in mineralogy, when a 

 mineral is in its natural position or 

 place ; in its native site. 



SKI'DDAW SLATE, (from Mount Skid- 

 daw.) The Skiddaw slates form 

 the lower division of the Cambrian 

 group. They are of a thickness of 

 6,000 feet. 



SKO'LEZITE. An earthy mineral, nearly 

 allied to Thomsonite. It occurs at 

 Pargas, in Finland. 



SKO'EODITE. (from GicopoSov, garlick, 

 Gr.) A mineral of a leek-green or 

 brown colour ; an arseniate of iron. 

 Before the blow-pipe it fuses, giving 

 out a smell of garlick, from which 

 circumstance it has obtained its 

 name. 



SKO'KZA. The epidote skorza of Brong- 

 niart ; epidote arenace of Haiiy. A 

 variety of epidote. See Epidote. 



SLAG, (schlacke, Germ, slagg, Dan.) 

 The drop or recrement of metal. 



SLATE. A kind of clay, of a structure 

 termed schistose, which admits of 



being split into thin layers of con- 

 siderable extent. Slate is commonly 

 of a bluish or greenish colour, with 

 a silky lustre. It consists of silex 

 50'0, alumina 25*0, oxide of iron 

 11-3, manganese 1-6, potash 4-8, 

 carbon 0*3, water 7*5. It is opake ; 

 may be scratched by the knife ; and 

 fuses into a blackish slag. 



SLATE CLAY. See Shale. 



SLA'TY. Kesembling slate ; containing 

 slate; composed of parallel thin 

 plates which admit of being sepa- 

 rated by splitting. 



SLATE SYSTEM. This group is sub- 

 divided into, 1st, the Plynlymmon 

 rocks, consisting of grauwacke and 

 grauwacke slate, with beds of con- 

 glomerates, the thickness of the 

 whole being estimated at several 

 thousand yards. 2nd, The Bala 

 limestone, a dark limestone asso- 

 ciated with slate, containing shells 

 and corals. 3rd, The Snowdon 

 rocks, consisting of fine-grained 

 slates, of various shades of colour, 

 and of fine and coarse grauwacka 

 and conglomerate. In the strata 

 of the slate system are found the 

 most ancient organic remains. 



SLI'CKENSIDES. 



1. A provincial name for a variety 

 of galena. 



2. "It sometimes happens," says 

 Mr. Phillips, " that the vein- stuff 

 of each wall of a vein is nearly 

 compact, both so completely occu- 

 pying the vein, that they meet 

 together in close contact in the 

 middle. The two faces in contact 

 appear as though they had been, 

 polished, and are ribbed, or rather 

 fluted, horizontally ; and the face of 

 each is sometimes covered by a 

 remarkably thin coating of lead ore; 

 these planes, when separated, are 

 the slickensides of the mineralogist. 

 The edges of the strata on the sides 

 of faults frequently present that 

 polished appearance known to miners 

 under the name of * slickensides.' " 



SLOTH. The Bradypus of Linnasus, 



