CLAYS OF BURLINGTON COUNTY. 381 



deposit showing 16 feet of clay (PL XL, Fig. 2), underlain by 

 white sand and covered by 4 to 6 feet of Pensauken gravel. 1 It 

 is black, micaceous, and the clay layers are separated by thin 

 laminae of white sand. Pyrite concretions are very abundant, and 

 owing to' the large amount of carbonaceous matter, care has to be 

 exercised in the early stages of burning, not to' push the firing too 

 fast, otherwise the bricks are liable to swell and crack. Drying 

 takes about 48 hours. As a matter of fact the clay is not used 

 alone but is mixed with a certain proportion of surface loam of 

 Pleistocene age. 



The black clay (Lab. No>. 652) has the following physical 

 characteristics : 



Water needed for tempering, 27.8 per cent. ; air shrinkage, 7 

 per cent.; average tensile strength, 168 pounds per square inch. 



Cone 03 13 



Fire shrinkage, 5 % 5.6 % 5-6% 



Absorption, 11.89% ' 7-12% .... 



Color, pale red pale red pale red 



Condition, steel-hard .... 



The addition of the loam improves its color-burning properties 

 and renders it more porous. The material burns to a good red 

 brick, of moderate absorption, but is too- coarse-grained to make 

 a good smooth pressed brick. 



Kinkora. — At Murrell Dobbins' brickyard the upper portion of 

 the sandy laminated Raritan clays are shown, but most of the 

 clay used comes from the overlying Clay Marl I. An analysis of 

 the laminated Raritan clay was given by Dr. Cook 2 as follows : 



Analysis of clay from Murrell Dobbins' yard, Kinkora. 



Sand, 31.80 



Combined silica (SiO?) 25.50 



Alumina (A1 2 3 ), 17.70 



Ferric oxide (Fe 2 3 ), 6.40 



Lime (CaO), 0.16 



1 Since this was written, continued excavation into the hillside has shown 

 a few feet of Clay Marl I on the Raritan clay and beneath the gravel. The 

 contact is distinctly marked by an abrupt change in the character of the 

 deposits and a line of nodules, but owing to the sameness of color of the two 

 formations here it is not obtrusive. H. B. K. 



2 Clay Report, 1878, p. 241. 



