CLAYS OF NEW YORK S25 



I 



SHALES OF NEW YOKK 



These form an enormous series of deposits in tlie southern region 

 of the state, as well as some of the central portions. 



The origin of shale has already been mentioned (p. 502). From 

 the fact that they were deposited in the sea they are usually much 

 more extensive than the. Quaternary clays immediately underlying 

 the surface. 



The shales found in 'New York state are in every case quite 

 impure, and often silicious, indeed are at times interbedded with 

 thin layers of sandstone. Owing to their consolidated nature the 

 shales have to be first ground in order to develop their plasticity; 

 the finer the grinding the more plastic the mass. It has also been 

 found that in some cases the finer gTinding of the shale produces a 

 vitrified brick at a temperature that formerly did not allow this, 

 the brick made from the coarser shale showing 6^-7^ absorption. 



Shales exhibit a great variation in hardness ; this fact shows itself 

 specially during the gTinding process. As has been stated in an- 

 other place, shale is only a consolidated clay. Sometimes this hard- 

 ening or consolidation has occurred by the weight of the overlying 

 beds alone, while at other times the clay particles have become more 

 or less cemented together. It is obvious, therefore, that those, 

 shales hardened by the former circumstance will fall apart more 

 readily in the grinding pan, and tend to yield a more plastic mass. 



So far as the shales have been used and tested, the Devonian 

 shales seem to work best for a vitrified product, as the points of in- 

 cipient fusion lie from 250 to 300° F. apart. 



The Salina shales make a good strong brick if thorough vitrifica- 

 tion is not desired, for they are often calcareous. 



The Medina shales, particularly the weathered portions, are util- 

 ized in Ontario for making pressed brick and give good results. The 

 deposit continued across west central New York awaits develop- 

 ments 



