524 REPORT ON NATIONAL MUSEUM, 188G. 



Orbitoides limestone. A fossiliforoiis limestoue abundant in the upper Eocene 

 formation in the Southern States. 



Perch. lu Philadelphia, 22 cubic feet are called a perch. A perch of masonry 

 contains 24| cubic feet, lf)| x 1^ x 1. It is usually taken at 25 cubic feet. The 

 term is falling into disuse. 



Plucky. A term often used by stone-cutters to designate stones -which under the 

 chisel break away in irregularly conchoidal chips, and which are therefore diffi- 

 cult to trim to a line or to bring to a perfect surface. Common in compact 

 and impure limestones. 



Porphyry. Any stone composed of an extremely fine grouudmass in which larger 

 crystals are developed. 



Porpliyritic. When a rock consists of a compact or fine and evenly crystalline 

 groundniass, throughout which are scattered larger crystals, usually of feld- 

 spar, the structure is said to be porphyritic. This structure is quite common in 

 granite, but is not particularly noticeable, owing to the slight contrast in color 

 between the larger crystals and the finer groundmass. It is most noticeable in 

 such rocks as the felsites, in which, as is the case with some of the "porphy- 

 ries " of eastern Massachusetts, the groundmass is exceedingly dense and compact 

 and of a black or red color, while the largo feldspar crystals are white and 

 stand out in very marked contrast. This structure is so striking in appearance 

 that rocks possessing it in any marked degree are popularly called porphy- 

 ries whatever may be their mineral composition. The term porphyry is said 

 to have been originally applied to certain kinds of igneous rocks of a reddish 

 or purple c(dor, such as the celebrated red porphyry or " roseoantico" of Egypt. 

 The word is now used by the best authorities almost wholly in its adjective 

 sense, since any rock may possess this structure whatever its origin or composi- 

 tion may be.* 



Putty po"wder, or polishing putty, is a fine whitish powder, cousisting in the com- 

 mercial form of about equal parts oxide of tin and lead. Used in polishing 

 stone and glass. 



Quarry. Any opening in a ledge for taking out stone. 



Quarry -water. All rocks when first taken from the quarry contain more or less wa- 

 ter, which evaporates on exposure, leaving the stone considerably harder. In 

 sandstones this quarry water is considered by Newberry to bo a solution of 

 silica (Rep. of Judges, Group 1, p. 127). Its composition probably varies greatly 

 in (lifiereut classes of rocks. (See p. 3H9.) 



Rhyolite. A i)ost-Tertiary volcanic rock of the composition of granite. 



Rift. The direction in a rock par.allel to the lamination or foliation, and along which 

 it splits with greatest ease. 



Rubberstone. A sliarp-gritted Ohio or Indiana sandstone used for sharpening shoe- 

 knives ; ;ilso called a shoe-stone. 



Rubble maisonry. Rough, nnsqnared stones laid in iiregnlar courses. 



Saccharoidal. llnAiug a. gi-ain and structure like that of loaf sugar. Common in 

 crystalline limestone. 



Salt veins. A terra applied by the quairymen to the coarse granite veins from 2 

 inches to 2 or more feet thick, and which are found intersecting granites and 

 older crystalline rocks. 



Sv ab. A local term used in certain sandstone quarries in Iowa. The stone is very 

 massive and is broken from the quarry in irregular lumps by blasting. These 

 lumps are then trimmed down to a slia[ie approximately rectangular by means 

 of heavy picks. Tliis process is deuouiinated scabhhi;/. 



Sap. The term originated from imagined analogy between the decomposed layer 

 and the sap wood of trees. A term applied to the stained and worthless por- 

 tions of the stone extending inward from the point. 



* Hull, I'liihling and Ornamental Stones, p. 75. 



