COMPOSITION, DISTRIBUTION, AND EXCAVATION OF GYPSUM. 29 



Excavation and handling of rock gypsum. Deposits of rock gypsum, 

 are worked either in open quarries or in mines, the choice depending 

 on the thickness of the bed, its dip, and the amount of stripping neces- 

 sary. Usually work is commenced in an open cut on the outcrop of 

 the gypsum bed. After the entire available face on the property has 

 been opened in this manner, it is necessary to decide whether the work- 

 ings can be most economically driven as underground tunnels or slopes, 

 or by stripping and open-cut work. At the Severance quarries at 

 Fayetteville, N. Y., over 40 feet of shale and limestone stripping is 

 removed, but the total thickness of gypsum beds shown here is 60 feet; 

 and such heavy stripping could not be justified in order to work thinner 

 beds. 



Under ordinary conditions the cost of quarrying gypsum may range 

 from 20 to 35 cents per ton, as compared with 40 to 60 cents per ton 

 for mining it. In mining, large pillars must be left at frequent intervals, 

 and timbering is necessary, in addition, for extensive workings. 



Mining methods. The mining methods practiced at a typical Kansas 

 locality are described * as follows by Crane : 



"As a rule, there is little or no system employed in laying out the 

 workings. Main lines of haulage are run as continuations of the sur- 

 face drifts, other openings being run parallel with them on further de- 

 velopment, or run from the foot of a shaft sunk to the workable deposit. 

 On one or both sides of the haulageways rooms are driven, which 

 often run together, thus leaving odd and very irregularly shaped pillars. 

 Long working-faces are often formed, which must be again broken 

 by passages forming pillars for the support of the roof. Usually, how- 

 ever, single rooms, more or less irregular in shape, are opened up and 

 worked until the handling of the product becomes inconvenient, when 

 new and more advantageously placed openings are begun. 



" The mine in question was opened by an adit, which, beginning on 

 a fairly steep hillside, at a point on a level with the second floor of 

 the mill, extends into the hill for a distance of about 1000 feet. No 

 special attempt was made to align the adit, consequently considerable 

 useless work was done. For the first 400 feet the adit runs approxi- 

 mately north; the next 300 feet shows a marked variation from the 

 north-and-south line. An attempt was then made to rectify the devia- 

 tion by driving a right-angled offset 25 feet in length; the remaining 

 300 feet was driven approximately parallel with the first 400 feet. 



* Crane, W. R. The gypsum-plaster industry of Kansas. Eng. and Mining 

 Journal, p. 442, March 17, 1904. 



