503 NEW YOEK STATE MUSEUM 



are known as shale. Shales simply represent the finest clay sedi- 

 ment, which has been deposited in those parts of the ocean which 

 are very quiet and has become consolidated by the pressure of other 

 sediments laid upon it. In some hard shales there is probably also 

 some cementing material between the grains. 



In the later discussion of the chemical and physical properties of 

 clay whatever is said of clay will also apply toi shalei, unless it be 

 otherwise stated. 



Shales when ground up and mixed with water generally produce 

 a plastic mass similar to common clays. If simply placed in water, 

 however, they do not usually fall to pieces as an ordinary clay does, 

 or, in other words, they do not slake. Shales may be either highly 

 refractory or extremely fusible, and both forms of this material 

 are of commercial value. Some of the most refractory material 

 mined in the United States, as for instance the fire clays found 

 at Denver Col., or those in Pennsylvania, are shales. The chief 

 use of shales in the United States is in^the manufacture of paving 

 bricks. Those of IsTew York state are treated in a separate 

 chapter. 



