188 THE GKANITES OF MAINE. 
Motion. A term used in granite regions to designate small paving-block quar- 
ries. (See PL XII, B.) 
Ophitic. A term applied to microscopic rock texture to designate a mass of 
longish interlacing crystals, the spaces between which have been filled 
with minerals of later crystallization. 
Pegmatite. A very coarse granite occurring in irregular dikes or lenses in 
granites and some other rocks. (See p. -14. ) 
Plagioclase. A term applied to all those feldspars that are not potash feld- 
spars. 
Polarized light. Light whose vibrations, unlike those oi' ordinary light, which 
are in all directions, are in only one plane. Polarized light is used in the 
microscopic study of rocks. 
Porphyritic. A term applied to rock texture to designate the presence of iso- 
lated crystals in a general mass (matrix or grouudmass) of finer material. 
(Sco p. 20.) 
Random stone. A term applied by quarrymen to quarried blocks of any dimen- 
sions. (See definition of dimension stone.) 
Rift. A quarrymen's term to designate an obscure microscopic cleavage in] 
granite which greatlj facilitates quarrying. (See p. 26 and tig. 28.) 
Salt-iioksk. Quarrymen's term for aplite. 
Sap. Quarrymen's term for ferruginous discoloration along sheet or joint 
surfaces. 
Schist. A rock made up of flatfish particles arranged in rough parallelism, 
some or all of which have crystallized under pressure. 
Schistositv. The quality of being like a schist. 
Seam. Quarrymen's term for joint. 
Secondary minerals. .Minerals whose presence is due to the alteration of the 
original minerals. 
Sedimentary. A term designating those rocks that consist of particles depos- 
ited under water. 
Segregation. The scientific term for "knot;" a collection of material separate! 
from other material. 
Sericite. A more or less fibrous form of muscovite (potash mica), often result- 
ing from the alteration of feldspar. 
Shakes. Quarrymen's term to designate a somewhat minute close-joint struc- 
ture, which forms along the sheet surface as a result of weathering. 
(Seep. 40.) 
Sheet quarry. A quarry in which the granite lies in sheets, crossed by wide- 
spaced sleep joints. 
Su< kensides. The polished and grooved faces of a joint or bed caused by 
motion and friction. 
Specific gravity. The weight of a rock or mineral compared to that of a body 
of distilled water of the same bulk. (See p. 21.) 
Stratified. A term applied to rock consisting of originally horizontal beds or 
strata. 
Strike. The direction at right angles to the inclination of a plane of bedding, 
a sheet, or joint, etc. 
Stripping. The material (sand, clay, soil, etc.) overlying a rock of economic 
value, which must be removed before quarrying. 
