384 CLAYS AND CLAY INDUSTRY. 



The run of the bank mixed with screened gravel gives the best 

 results. The bottom black clay (Lab. No. 648) is fat and greasy 

 and has much mica and organic matter, and does not work well 

 alone. The greensand is also a dangerous element and causes a 

 swelling and bursting of the brick unless they are set in the kiln 

 dry and burned slowly. The bottom black clay has a high air 

 shrinkage, but its fire shrinkage is not excessive, as can be seen 

 by the following characters : Water required for mixing 32.8 

 per cent. ; air shrinkage, 9 per cent. 



Burning test on bottom black clay, A. Reeve, Maple Shade. 



Cone 01 1 



Fire shrinkage, 3 % 4 % 



Absorption, 12.62% 10.06% 



Color, red red 



Condition, barely steel-hard 



The run of the bank showed lower air shrinkage, but the fire 

 shrinkage is not much different, and the mixture can probably be 

 burned somewhat faster than the black clay can. The physical 

 characters of the brick mixture (Lab. No 1 . 647) are also given 

 herewith : Water required for mixing, 28.6 per cent. ; air shrink- 

 age, 7.5 per cent. ; average tensile strength, 282 pounds per square 

 inch. The clay behaved as follows in burning": 



Burning test of bottom black clay, A. Reeve, Maple Shade. 



Cone 1 



Fire shrinkage, 4.5 % 



Absorption 10.58% 



Color, red 



Condition, steel-hard 



The clay becomes viscous at cone 8. This mixture works well 

 on a stiff-mud machine. 



Of the unworked areas the following may be enumerated and 

 their physical characters given. 



Bndgeboro. — A bed of Clay Marl I outcrops along a tributary 

 to Rancocas creek, about one-fourth mile southeast of Bridgeboro 

 (Loc. 131). The clay in appearance is not unlike that in the 



