BU1LDIX(; AND OKNAMKN'rAI> tS'lONES. 525 



Sculp. 'I'o sculp wljitcs is to ))iv;i!< n[» tlio l;ln^(^ blocks iiilo long slahs, stiitiil)h) to 



si)lil. 

 Segregated. A term ;i[)iilictl to tlio veins Mid nodiiliir nuisscs of liner or coarser 



texture tliiit liavo fornnMl in j^ranitc and other crystalline roi;ks ; as for I'xani- 



plo, the black patches in i^ranite. 

 Serpentine. A rock composed of hydrons magnesia silicate. 

 Shell limestone. Rock composed of cousolidatctl shells. 

 Siliceous. Contaiuiuit silica. 

 Spalls. This is a term which is usi'd (juite generally by sionc-cuttt^'s to denote the 



chips and other waste mat(!rial cut from a block in process of dressing. 

 Spider-web. A term applied to the wa\'y lines in the Ohio sandstones, and which 



are caused by stains of iron o\ide. Freiiueutly seen iu sawed stonea, especially 



where the lauiiuatiou is slightly obliiiue or irregular. It is very like the grain 



of wood which shows in a planed l)oard. 

 Split rock. This term a[)plies to those rocks possessing tabular structure, or which 



cleave easily in the lines of lamination, and are consequently ai)plicable to the 



lirejiaration of llagging aud for curbstones. 

 Stalactitic marble. This is a marble which is formed by the dci)osit of lime car- 

 bonates from waters percolating into cavities or caves. 

 Strata. Layers or beds of rock of the sanu^. kind lying ono upon another. 

 Stratified; bedded. Composed of layers or beds lyiug parallel to one another, as is 



so frec^uently seen iu sandstone and limestone. When the strata are line and 



leaf-liko the structure is called lamiuated or shaly. 

 Stieaked. Having some of the mineral constituents so arranged as to give tlu^ rock 



a striped or streaked appearaiu'c. In the eruptive rocks this structure isoflen 



produced by the flowing of the mass iu a partially cooled condition. It is best 



seen in obsidian, rhyolite, and ([uartz por])hyries. 

 Stock. The useful rock taken from a quarr^'. 



Strike. The direction in strata at right angles to the dip, or the co\irse of a horizon- 

 tal lino on the surface of inclined beds. 

 Syenite. Agranular massive rock with the structure of a granite, but containing 



uo (] uartz. 

 Trachyte. A j)ost Tertiary volcanic rock of the composition of syouitc. 

 Trap or trap rock. (See Dikes aud Greenstone.) The luime applies to the manner iu 



which a rock occurs, and i.s not itself a name of specilic value. 

 Travertine. A calcareous rock (kqiosited by water from solution, and which was 



used as a building stone in Kouu\ (See text.) 

 Verde antique. Auti(]^uo green. A rock coiu[>oscd of a mixture ol" serpentine and 



limes ton(^. 

 Vitreous or glassy. These terms are applied to rocks that have a structure like glass, 



as obsidian. Rocks of this type are at prescut little used for any kind of work. 



