BUILDING AND ORNAMENTAL STONES. 525 



Sculp. To sculp slates is to break up the large blocks into long slabs, suitable to 

 split. 



Segregated. A term applied to the veins ami nodular masses of liner or coarser 

 texture that have formed in granite and other crystalline rocks ; as for exam- 

 ple, the black patches in granite. 



Serpentine. A rock composed of hydrous magnesia silicate. 



Shell limestone. Rock composed of consolidated shells. 



Siliceous. Containing silica. 



Spalls. This is a term which is used quite generally by stone-cutters to denote the 

 chips and other waste material cut from a block in process of dressing. 



Spider-web. A term applied to the wavy lines in the Ohio sandstones, and which 

 are caused by stains of iron oxide. Frequently seeu in sawed stones, especially 

 where the lamination is slightly oblique or irregular. lb is very like the grain 

 of wood which shows in a planed board. 



Split rock. This term applies to those rocks possessing tabular structure, or which 

 cleave easily in the lines of lamination, and are consequently applicable to the 

 preparation of flagging and for curbstones. 



Stalactitic marble. This is a marble which is formed by the deposit of lime car- 

 bonates from waters percolating into cavities or caves. 



Strata. Layers or beds of rock of the same kind lying one upon another. 



Stratified ; bedded. Composed of layers or bods lying parallel to one another, as is 

 so frequently seen in sandstone and limestone. When the strata are line and 

 leaf-like the structure is called laminated or shaly. 



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

 a striped or streaked appearance. In the eruptive rocks this structure is often 

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

 seen in obsidian, rhyolite, and quartz porphyries. 



Stock. The useful rock taken from a quarry. 



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

 tal line on the surface of inclined beds. 



Syenite. A granular massive rock with the strqeturo of a granite, but containing 

 no quartz. 



Trachyte. A post -Tertiary volcanic rock of the composition of syenite. 



Trap or trap rock. (See Dikes and Greenstone.) The name applies to the manner in 

 which a rock occurs, and is not itself a name of specific value. 



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

 used as a building stone in Rome. (See text.) 



Verde antique. Autiquo green. A rock composed of a mixture of serpentine and 

 limestone. 



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

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



