CLAYS OF BURLINGTON COUNTY. 377 



the Delaware river. The stripping is used for filling, and the 

 close proximity of the clay to the river permits it to be shipped by 

 water. 



The mottled clay (Lab. No. 622), representing the run of the 

 bank, is fairly plastic, although containing some coarse grit, and 

 has the following physical properties : Water required to temper, 

 22 per cent. ; air shrinkage, 5.3 per cent. ; average tensile strength, 

 104 pounds per square inch. Its behavior in burning was as 

 follows : 



Burning tests on mottled clay from J. IV. Paxson Company's pit, Bridgeboro. 



Cone 05 3 5 8 



Fire shrinkage, 1.3% 47% 47% 6.7% 



Absorption, 13.81% 988% 9.13% 2.96% 



Color, pale red light red dark red gray 



Condition barely steel-hard steel-hard 



This clay, which is probably to be classed as a semifire clay, is 

 used for making terra cotta and for foundry purposes. 



The whitish sandy clay (Lab. No'. 630) shows a marked dif- 

 ference in its character. It is less coherent, with scattered white 

 mica scales, and slakes very fast. It takes somewhat more water 

 in mixing, viz, 30.8 per cent., but its air shrinkage is less, being 

 but 4.3 per cent. The average tensile strength is higher, viz, 119 

 pounds per square inch. Its low fire shrinkage is seen from the 

 fact that at cone 10 it is only 2.7 per cent., the bricklet having an 

 absorption of 7.99 per cent, and a light-buff color. It was steel- 

 hard. A sample was burned up to cone 15, and the fire shrinkage 

 of this was but 3 per cent., and its absorption 2.96 per cent. It 

 burned gray with brown specks. Its fusing point was not de- 

 termined, but it contains too much sand to be highly refractory. 



A dry-press tile, screened to 80-mesh and burned at cone 8, 

 was steel-hard, buff-colored, but still slightly absorbent. 



This last mentioned clay should make a good material to add to 

 terra cotta in order to lower its shrinkage. It is more refrac- 

 tory than the mottled clay from the same bank, but there is much 

 less of it available. 



Florence. — Clays apparently similar to those just described 

 occur in the vicinity of Florence. They were formerly dug by 



