346 CLAYS AND CLAY INDUSTRY. 



but one from the Hackensack district (Loc. 291) was well vitrified 

 at cone 01. No refractory clays are found in this group, for 

 in fact most of them fuse quite readily. 



Uses. — These clays are worked at a number of localities in 

 the northern part of the State, including" Somerville, Plainfield, 

 Berkeley Heights, Singac, Mountain View, Morristown, Whip- 

 pany, Hackensack, etc. Many of them could be worked into 

 draintile, and the finer grained layers used for common red 

 earthenware. One deposit near Linden is extensively drawn 

 upon for the last mentioned purpose. Vitrified brick have been 

 made at Whippany. 



Second group, chiefly of Cape May age. 



Texture. — Most of the clays of this series are gritty, loamy 

 or even very sandy. Those around Trenton also contain scattered 

 pebbles and cobbles. Those underlying the terraces along the 

 lower Delaware are commonly loamy. When the pebbles are 

 abundant it becomes necessary to' remove them either by screen- 

 ing the clay or else by crushing in rolls. Judging from the tests 

 obtained, clays in adjoining pits may show some difference in 

 their behavior when fired, as for example the clays from localities 

 180 and 181, near Millville, which represent pits on opposite sides 

 of the river not over 1,000 feet apart. 



Slaking. — Many of these clays fall to pieces rapidly when 

 thrown into water, but others even though sandy, slake slowly 

 because the clay particles in them are evenly distributed and hold 

 the sand grains together. These same ones will usually dry to a 

 hard mass. 



Air shrinkage. — In the 14 samples measured the air shrinkage 

 was found to range from 3.6 per cent, up to 10 per cent., with 

 an average of 6.04 per cent. The air shrinkage of 9 of the 14 

 lay between 5 and 7 per cent. 



Water for tempering.— -The amount of water required to mix 

 the material to a plastic mass ranged from 21.4 per cent, to 37.1 

 per cent, with an average of 27.3 per cent. Unlike Clay Marls 

 I and II none of these clavs can be molded as taken from the 



