CLAYS OF KEW YORK 827 



the slialy layers is miimportant. (Hall. Geology of the Jftli dis- 

 trict of New Yorh. p. 38) 



The shale beds are, however, well developed at Lewistoiij where 

 they are exposed in the sides of the gorge on both the American 

 and Canadian shore. Erom this point they extend eastward and are 

 to be seen at a number of points in the terrace escarpment. 



The shale is rather soft and crumbly, and in places contains 

 abundant mica flahes. It is highly ferruginous and weathers to a 

 red clay, which is more plastic than the mass produced by grind- 

 ing the partially weathered shale and mixing it with water. 



This material has not thus far been utilized in ISTew York state, 

 yet it is extensively employed at several localities in Ontario, nota- 

 bly Beamsville, for the manufacture of pressed brick. 



A sample collected from the exposures at Lewiston was tested 

 with the following results. 



The partially weathered shale gave a lean mass when mixed 

 with 16/^ of water. The air shrinkage of the bricks was 3^, and 

 the tensile strength of the air-dried clay was 15 pounds a square 

 inch. 



The clay contains .Q'/o of soluble salts. In burning it shrinks 

 very slowly, and at 1 the shrinkage was only 6/^. At this point 

 the shale had vitrified and showed a deep red color. Incipient fusion 

 occurred at .04, the clay burning bright red. It became viscous 

 at above 4. 



Its composition is: 



Silica 59.50 



Alumina 20 . 60 



Terric oxid 8 . GO 



Lime 80 



Magnesia .35 



Alkalis 3.60 



Water 5 . 50 



Total 98.35 



