GYPSUM 409 



in various formations ran<i;in<j^ from tho Sihui'in \\\) to 'I^Miiarv. 

 In New York extensive beds of g^^)sum are found in (he Silii- 

 rian formation; in Ohio and Michigan they occur in the Car- 

 boniferous; and in Iowa and Kansas tliey are Cretaceous. 

 Gy]:)sum is also widely distributed geographically. In the 

 United States it is found in Arizona, California, Colorado, 

 Iowa, Kansas, Michigan, Montana, Nevada, New Mexico, New 

 York, Ohio, Oklahoma, Oregon, South Dnkota, Texas, Utah, 

 Virginia, and Wyoming, and is mined in all these states exce])t 

 Arizona, Missouri, and New Mexico. It is found in Arabia, 

 Austria, Bohemia, Canada, Eg^T^t, England, France, Germany, 

 Italy, Norway, and Persia. 



The use of g>^sum was kno^\^l at a very early period, for 

 the Greeks were familiar with it, as shown by the writings of 

 Theophrastus and Pliny. Gj^Dsum in its ground, uncalcined 

 state is used chiefly for land plaster, a fertilizer. In its cal- 

 cined form, as plaster of Paris, it has extensive and varied uses. 



Ground plaster has long been used as a fertilizer. Virgil 

 wrote concerning the value of gj^^psum on cultivated lands. 

 Benjamin Franklin called attention to the value of gypsum as 

 a fertilizer for grass by sowing land plaster in a clover field, so 

 as to form the sentence, ''This has been plastered with gyp- 

 sum," the letters showing by the height and color of the clover 

 where g^^Dsum had been so^\^l. 



The theories of the action of gj^sum as a fertilizer have 

 been man3^ Sir Humphr^^ Davy and others before and after 

 his time have regarded g^^^sum as a direct source of plant food. 

 It is now thought that g^'psum acts as a fertilizer in three ways, 

 one mechanical and two chemical: 



(1) The gj^sum by mechanical action flocculates loose 

 soils. 



(2) G}T)sum as pointed out by Storer has nearly one half 

 its weight in oxygen and gives this up to many substances, and 

 so may act upon nitrogenous and carboniferous substances in 

 the soil. 



(3) G3T)sum decomposes the double silicates in the 

 earth, setting free potash as a soluble silicate. 



By this means the potash hi solution reaches the roots of 

 the plants. Soils with abundant potash do not need land 



