GYPSUAI DEPOSITS OF NEW YORK' 59 



CHARACTER OF THE GYPSUM IN NEW YQRK; CHEMICAL 



ANALYSES 



Within the long stretcli of Sahna strata from Madison to Erie 

 county are included gypsum deposits of different physical and 

 chemical characters. These variations are conditioned mainly by 

 the relative proiportions and nature of impurities present and to a 

 lesser extent by the different conditions in which the gypsum itself 

 is found. 



While the deposits all belong to the general class of rock gypsum, 

 from the descriptions of the individual deposits aikeady given it is 

 possible tO' distinguish two types that seem to be separate in their 

 occurrence and may have originated under somewhat different con- 

 ditions. The first of these is represented by the dense firm gypsum 

 in which the impurities are evenly distributed so as to give the 

 appearance of a more or less homogeneous mass. This is the usual 

 rock g}^psum which forms the basis of the calcined plaster industry 

 in New York and in most places elsewhere. It consists of a ground 

 mass of finely divided gypsum fibers or elongated acicular crystals 

 in felted arrangement, with occasional larger individuals that stand 

 out prominently by their briMiant cleavage surfaces. The other 

 type is characterized by a loosely cemented aggregate of gypsum 

 and sihale, the two constituents being plainly discernible. The gyp- 

 sum is usually in large crystals or crystal aggregates which by 

 themselves are transparent and quite free from impurities. The 

 deposits of this type are built up of successive thin layers of the 

 selenite and shale. When the mass is exposed to the weather, the 

 shale decomposes quickly and fal'ls away from the gypsum so that 

 in outcrops it may have the semblance of a high grade deposit. 

 This type is known to the gypsum miners as " ashes," owing prob- 

 ably to the grayish color and .powdery nature of the shale. It was 

 quite extensively worked at one time for land j^laster, but is evi- 

 [ently unsuitable for calcination. 



The chemical composition of the gypsum found in different sec- 

 tions of the Salina outcrop is shown by the accompanying detailed 

 malyses of samples which were collected during the recent field 

 ^ork. The samples represent the run-of-mine gypsum as now 

 itilized, having been collected from the stock bins of the different 

 lills. The analyses were made by George I^. Willcomb. 



