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altered or metamorphic stratified rock. Its name Is derived 

 from frequently presenting contrasts of colour, like the skinof 

 some serpents. 



Shale. A provincial term, adopted by geologists, to express an indu- 

 rated slaty clay. Etym., German schalen, to peel, to split. 



Shell Marl. A deposite of clay, peat, and other substances mixed 

 with shells, which collects at the bottom of lakes. 



Shi7igle. The loose and completely water- worn gravel on the sea- 

 shore. 



Silex. The name of one of the pure earths, being the Latin word for 

 flint, which is wholly composed of that earth. French geolo- 

 gists have applied it as a generic name for all minerals com- 

 posed entirely of that earth, of which there are many of dif- 

 ferent external forms. 



Silicious. Of or belonging to the earth of flint. Etym., silex, 

 which see. A silicious rock is one mainly composed of 

 silex. 



Silt. The more comminuted sand, clay, and earth, which is trans- 

 ported by running water. It is often accumulated by currents 

 in banks. Thus the mouth of a river is silted up when its 

 entrance into the sea is impeded by such accumulation of 

 loose materials. 



Simple Mineral. Individual mineral substances, as distinguished 

 from the rocks, which last are usually an aggregation of simple 

 minerals. They are not simple in regard to their nature, for, 

 when subjected to chemical analysis, they are found to consist 

 of a variety of different substances. Pyrites is a simple mineral 

 in the sense we use the term, but it is a chemical compound 

 of sulphur and iron. 



Stalactite. When water holding lime in solution deposites it as it 

 drops from the roof of a cavern, long rods of stone hang 

 down like icicles, and these are called stalactites. Etym., 

 tfTaXa^w, stalazo, to drop. 

 Stalagmite. When water holding lime in solution drops on the 

 floor of a cavern, the water evaporating leaves a crust com- 

 posed of layers of limestone: such a crust is called stalagmite, 

 from tfroChay^a, stalagmu, a drop, in opposition to stalactite, 

 which see. 



