CLAYS OF CUMBERLAND COUNTY. 413 



the variation in thickness is caused by a rise in the level of the 

 bottom sandstone layer towards the south end of the pit. 



The physical properties of the sample tested (Lab. No. 619) 

 were as follows : water required to mix, 30 per cent. ; air shrink- 

 age, 7 per cent.; average tensile strength, 133 pounds per square 

 inch. In burning it behaved as follows : 



Burning test of clay from Erickson's pit, Bridgeton. 



Cone 05 1 3 5 



Fire shrinkage, 3.6% 5-3% 7-6% 7-6% 



Color, pale red red red red 



Condition, nearly steel-hard steel-hard 



Absorption, 14.81% 7-96% 5-57% 4-19% 



The clay alone, it is seen, burns quite dense at a moderately low 

 temperature, and, if molded stiff er, the total shrinkage could no 

 doubt be reduced. In actual practice the clay is mixed with sand 

 and molded quite wet, so that the total shrinkage in drying and 

 burning is about 14 per cent, and the brick has an absorption of 

 probably 14 or 15 per cent. It is claimed that the clay will not 

 stand molding in a stiff-mud machine without tearing. 



Certain layers of the clay are tougher and burn to a lighter 

 color than others in the bank, and unless they 'are thoroughly dis- 

 integrated in the machine they show on the broken surface of 

 the brick. This clay differs from most of those classed as Co- 

 hansey in burning red. Inasmuch as the clay occurs at an eleva- 

 tion of 40 feet, the height of the Cape May terrace, there is a 

 possibility that it belongs rather to the Cape May formation, 

 although on the whole, the stratigraphical evidence favors its 

 reference to- the Cohansey, 



Cape May Clays. 



Bridgeton. — A brick-clay pit (now idle) has been opened in 

 the Cape May formation on the west side of Cohansey creek one- 

 half mile south of Bridgeton (Loc. 190). The bed of clay, which 

 is at least 8 feet thick and possibly more, is fairly plastic but 

 gritty and contains numerous pebbles, some of them running up 



