THE MINING AND QUARRY INDUSTRY 79 



CO. the beds were penetrated between the depths of 1078 and 

 1296 feet, with a total thickness of 72 feet. The Lehigh salt 

 shaft at Leroy found 75 feet of gypsum at a depth of 390 feet; 

 and the Retsof shaft in Livingston co. found 47 feet at 613 feet 

 depth. 



The gypsum is associated with shales and thin limestones 

 which divide it into layers or beds. When the partings are not 

 too thick the entire deposit may be worked in a single breast. 

 Sometimes one or more layers are too impure to be utilized and 

 in underground opei*ations may be left as a foot or hanging 

 wall. 



When first extracted the gypsum is gray or drab in color, 

 becoming lighter on exposure with the evaporation of the ab- 

 sorbed moisture. Organic matter is usually the principal coloring 

 agent. Its influence is not particularly detrimental, for it is re- 

 moved by burning. The presence of iron in any quantity gives a 

 brownish or reddish appearance to the rock which is accentuated 

 in the calcined product. 



Productive operations in New York are limited to localities on 

 or near the outcropping deposits. The gypsum beds are often con- 

 cealed by glacial drift, whence the workings are frequently located 

 along the face of hills where the overburden is lightest. In the 

 eastern section open cut or quarry methods prevail. When the 

 beds have been followed back into the hill for some distance, if the 

 overlying strata are heavy the work may be continued under cover. 

 Mining is carried on at a few places through adit openings or 

 vertical shafts. With this method the workings require support 

 which is obtained by timbering, by storing the waste rock, or by 

 leaving pillars at intervals varying with the condition of the roof. 

 Underground tramways are frequently used in the mines for trans- 

 porting the rock. 



With the immense resources of crude material found within the 

 State, the development of the gypsum industry is dependent 

 altogether upon the demand for the diflferent products. For a long 

 time the principal market outlet was the land plaster trade, as the 

 gypsum was considered of little or no value for plaster of paris, 

 owing to its dark color. The employment of gypsum, however, for 

 the manufacture of wall plaster, stucco and other building purposes 

 has become widespread of late years, and a number of plants 

 making these products have been established in New York State. 

 This branch of the industry now consumes the larger part of the 



