197 



Shearing. — The puslnng of one portion of a mineral, or rock-mass, over 

 another, by intense pressure within the Eartli's Crust. 



S-peciJic Gravity. — The ratio between the weight of a substance and that 

 of an equal volume of water. 



Sliclxnsides. — A polished or striated surface caused by the rubbing 

 together of rock masses within the Earth's Crust. 



Spherulitic. — A nodular structure sometimes develoi^ed in certain volcanic 

 rocks. 



Stalactite. — Mineral matter, generally lime carbonate, suspended, icicle-^ 

 like, from the roof of a cavity. 



StaIag7nite.—M.merR\ matter which has accumulated in pyramids on the 

 floor beneath stalactites. 



Streak. — The colour of the powder of a mineral. 



Tuff. — A rock consisting of fragmentary material ejected from a volcano, 



Timn Crystal. See page 55. 



Vitreous. — Glass-like. 



Vugli. — A cavity in an ore-body. 



Wash-dirt. — That portion of an alluvial deposit tha^: contains the mineral 

 sought for. 



The correct pronunciation of geological names is a matter of 

 some diiEcLilty to persons who have not had the advantage of 

 trained tuition. The following hints may prove serviceable : — 



cli in such words as clialcedony , chiastolite, rliynchonella, must 

 be pronounced hard — that is, as if it were h. To pronounce it 

 like cli in church is quite incorrect. Chahasite may be pronounced 

 either way. 



g in gypsum., angile, plagioclase. Custom varies. There is a 

 tendency now to pronounce the g hard in all these words, and it 

 is recommended that this should be done. 



i in crmoid, trilohite. The English pronunciation as in mite is- 

 correct, and should be always followed. 



a in the fioal syllable of ortJioclase, plagioclase, diahase. It is 

 customary in English for the vowel of a syllable ending in silent e 

 to be lengthened, and tbis practice is usually followed in these 

 words ; thus craze, the s being pronounced as z. 



