62 ECONOMICAL MINERALOGY. 



When heated, the water is easily driven off ; and it then acts before the blowpipe like the 

 anhydrous sulphate of lime, being with difficulty fused into a white enamel. When the an- 

 hydrous powder is mixed with water, it forms a paste, which soon becomes solid, and is on 

 that account used for taking casts of statues, in stereotyping, &c. It is said to be better suited 

 for this purpose, by mixing it with about one third of its weight of carbonate of lime. The 

 Plaster of Paris, so called because it is found near that place, is such a compovmd ; and one 

 similar to it is found in the gypsum beds of Western New- York. The following is the com- 

 position of a specimen from Montmartre,* viz : 



Sulphuric acid, 41.00 



Lime, 29.39 



Carbonate of lime, 7. 63 



Insoluble matters, 3.21 



Water, 18.77 



Distinctive characters. Gypsum may be distinguished by its inferior hardness, and by 

 the action of acids, from the carbonate of lime, to whicli it often bears a resemblance. 



Almost all the different varieties of this species are sometimes found in one of our extensive 

 beds, and they are indiscriminately used for all those purposes to which gypsum is applied. 

 The chief uses are in agriculture as a manure, and in the preparation of stucco for walls. 



I shall describe the localities of this useful mineral in the alphabetical order of the counties 

 in which they are found. 



Albany County. Specimens of snowy gypsum have been found in the Helderberg moun- 

 tains ; and in the town of Coeymans, it occurs in an alluvial bed twenty or thirty feet thick, 

 where it eflSoresces on the sides of excavations made by rivulets and for roads. But its oc- 

 currence here is not in sufficient abundance to answer any useful purpose. Indeed it will be 

 presently observed, that the only important beds of this mineral are in the district bordering 

 on the Erie canal. 



Cayuga County. There are several important beds of gypsum in this county. Near 

 Troopsville, the earthy variety is found in large quantities. The same mineral is also abun- 

 dant at Cayuga Bridge ; but the largest number of beds have been opened south of the bridge, 

 and two miles north of Union Spring, and near the lake shore. Here are five plaster quar- 

 ries ; and to the east of these is another, owned by Mr. Thomson, which is remarkable for 

 the numerous seams of native sulphur which it contains. The thickness of the rock is from 

 eight to eighteen feet ; in many places it appears at the surface of the earth, and covers an 

 area of a mile square. A specimen of the plaster stone from this bed, when freed from water, 

 gave the following results, viz : 



Beudaiil. Traiti^ Elhnentaire de Mtncralogie, II. 469. 



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