Feet 



Inches 



i8 , 





3 

 3 

 3 



4 



21 



4 

 8 



I 



4 



4 



8 



4 





MINERAL RESOURCES OF THE STATE OF NEW YORK 97 



Earth 



Limestone 



Mud seams 



Limestone 



Mud seams (water bearing) 



Limestone 



Gypseous shale (ashes) 



Gypsum 



Limestone 



Ashe.s 



Gypsum 



Gypsum favors the superficial zone where water circulates readily 

 and most of the mines consequently are wet. As the beds deepen 

 toward the south on the dip and become covered by the Devonian 

 formations, the gypsum gives way to anhydrite, the material 

 commonly encountered in all deep borings and in the salt shafts and 

 wells several miles south of the Salina outcrop. The change from 

 g3rpsum with its content of 20 per cent or so of combined water to 

 the water-free and commercially worthless anhydrite takes place 

 quite abruptly, an increase of 10 feet of depth often marking the 

 complete passage from the one to the other. In mining, it is of 

 course useless to follow the seam beyond the limit marked by the 

 appearance of anhydrite in quantity. 



As a guide to the occurrence of gypsum in the field the outcrop 

 of the cherty beds of the Onondaga serves best, since it is usually 

 indicated by a sharp break in the topography or by a line of cliffs, 

 whereas the softer Camillus shales that lie below rarely are indicated 

 by topographic changes. The outcrop of the latter is just north of 

 that of the cherty beds and usually occupies a strip of low ground 

 a mile or more in width in which there are few exposiures. 



The outcrop of the gypsum does not lie at a constant level, but 

 ranges through an interval of 300 feet or so, between the approximate 

 limits of 750 feet which marks the elevation above sea level of the 

 beds at Oakfield and 400 feet which represents the low point along 

 the belt found at Seneca Falls, Seneca cotmty. The variation is 

 very gradual, scarcely perceptible within narrow limits, but appears 

 when the line of contract is traced, on the contour maps. It is an 

 inheritance from an early period, possibly dating back to the 

 Appalachian uplift and representing the last traces of differential 

 movement to the north of the main axis. 



Nature of deposits. The deposits consist of compact gypsum 

 usually of homogeneous appearance, which, however, varies con- 

 siderably from place to place in regard to purity. This is the rock 

 gypstim which forms the basis of the calcined plaster industry, as 



