SIM 



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SIP 



found necessary to describe under 

 one comprehensive name. For 

 this purpose Sir R. Murchison pro- 

 poses the term Protozoic, thereby 

 to imply the first or lowest forma- 

 tion in which animals or vegetables 

 occur. "Acting upon the principle 

 which guided "William Smith in 

 subdividing the oolitic system of 

 our island, I have named the rocks 

 of the Silurian system from places 

 in England and Wales, where their 

 succession and age are best proved 

 by order of superposition and im- 

 bedded organic remains, and have 

 termed them, in descending order, 

 the Ludlow, Wenlock, Caradoc, 

 and Llandeilo formations. Each 

 subdivision is characterized by a 

 corresponding suite of organic 

 remains, while the whole was for- 

 merly considered to be one assem- 

 blage, without definite sequence, 

 and was included under the names 

 greywacke or transition limestone" 

 The Silurian rocks consist of a 

 complete succession of fossiliferous 

 strata, interpolated between the old 

 red sandstone and the oldest slaty 

 rocks. In the lower or Cambro- 

 Silurian rocks we know of no 

 plants, with the exception of a few 

 sea-weeds : the animal remains are 

 those of zoophyta, polyzoa, brachi- 

 opoda, conchifera, gasteropoda, 

 cephalopoda, echinodermata, anne- 

 lida, and Crustacea (chiefly trilo- 

 bites). JS"o unquestionable remains 

 of any higher order of animals have 

 as yet been discovered. In the 

 upper Silurian rocks, many generic 

 forms make their appearance, not 

 met with in the lower series, and 

 many appear to have existed during 

 that period only. Two genera offish 

 have also been discovered, Onchus 

 and Plectrodus ; of the latter, three 

 species have been distinguished ; 

 the Plectrodus disappears with this 

 period. Jukes. 



SI'HPLE. (simplex, Lat. simple, Er. 

 semplice, 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 elementary, or undecomposed 

 substances : these are about 60 in 

 number, and are described under 

 the article " elementary substances." 

 The mineralogist and the geologist 

 consider those minerals as simple 

 and homogeneous, which present 

 no difference of qualities to our 

 senses throughout the mass, al- 

 though the chemist may discover 

 that such minerals are composed of 

 two or more elementary substances. 



SINI'STBAL. A term applied to shells, 

 where, in consequence of the heart 

 being placed on the right side, the 

 turns of the spiral are made to the 

 left. These shells are termed sm- 

 istral, or reversed. 



SI'NTEE. (sinter, Germ.) Calcareous 

 sinter is a variety of carbonate of 

 lime, and may be either stalactical, 

 tuberose, reniform, globular, cylin- 

 drical, tubular, branched, or in 

 large undulated masses. It is 

 composed, whatever may be its 

 form, of a series of successive layers, 

 concentric, plane, or undulated, 

 and nearly or quite parallel. 



Silicious sinter is an opaline 

 silica, deposited on the margins of 

 some hot springs. Some mineralo- 

 gists have established three sub- 

 species, namely, common silicious 

 sinter, opaline silicious sinter, and 

 pearly silicious sinter. 



SI'NTJATE. j (sinnatus, Lat.) In bot- 



SI'NUATED. j any applied to leaves 

 when the margins are cut into wide 

 rounded openings, as in the leaf of 

 the oak. 



SI'NUS. (sinus, Lat. a bag, sinus, Er.) 



1. In anatomy, a cavity or cell; a 

 narrow passage. 



2. In conchology, a groove or 

 cavity. 



SI'PHON. | (siphon sm&siphunculus, 

 SI'PHTJKCLE. j Lat.) An hydraulic 



