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Precipitate. Substances which having been dissolved in a fluid, are 

 separated from it by combining chemically and forming a solid 

 which falls to the bottom of the fluid. This process is the op- 

 posite to that of chemical solution. 



Producta. An extinct genus of fossil bivalve shells, occurring only 

 in the older secondary rocks. It is closely allied to the living 

 genus Terebratula. 



Pyrites. (Iron.) A compound of sulphur and iron, found usually in 

 yellow shining crystals like brass, and in almost every rock 

 stratified and unstratified. The shining metallic bodies, so 

 often seen in common roofing slate, arc a familiar example of 

 the mineral. The word is Greek, and comes from wup, pyr, 

 fire, because, under particular circumstances, the stone pro- 

 duces spontaneous heat and even inflammation. 



Quartz. A German provincial term, universally adopted in scientific 

 language, for a simple mineral composed of pure silex, or earth 

 of flints : rock-crystal is an example. 



Sandstone. Any stone which is composed of an agglutination of 

 grains of sand, whether calcareous, silicious, or of any other 

 mineral nature. 



Saurian. Any animal belonging to the lizard tribe. Etym. davpa, 

 saura, a lizard. 



Schist. Synonymous with slate. Etym., Schistus, adj. Latin ; that 

 which may be split, from the facility with which slaty rocks may 

 be split into thin plates. 



Seams. Thin layers which separate two strata of greater magni- 

 tude. 



Secondary Strata. An extensive series of the stratified rocks which 

 compose the crust of the globe, with certain characters in com- 

 mon, which distinguish them from another series below them, 

 called primary, and from a third series above them called ter- 

 tiary. 



Sedimentary Rocks, are those which have been formed by their ma- 

 terials having been thrown down from a state of suspension or 

 solution in water. 



Sclenite. Crystallized gypsum, or sulphate of lime — a simple mine- 

 ral. 



Serpentine. A rock usually containing much magnesian earth, for 

 the most part unstratified, but sometimes appearing to be an 





