382 CLAYS AND CLAY INDUSTRY. 



Magnesia (MgO), 0.65 



Potash (KaO), 1.54 



Soda (Na*0), 



Titanic oxide (Ti0 2 ) , 0.90 



Water (H 2 0), 11.80 



Moisture, 3.50 



Total, 99.95 



The Clay Marl Beds. 



A number of clay works are supported by the Clay Marl de- 

 posits in the northwestern part of the county. Some of these 

 use Clay Marl I and others Clay Marl II, while still others have 

 opened pits along the boundary between Clay Marls I and II, 

 and use a mixture. 



At many localities the Clay Marl is overlain by a ferruginous 

 sand or gravelly loam, of which a certain proportion is added to 

 the clay. In addition to the worked localities, samples were taken 

 from a number of outcrops of Clay Marl for the purpose of deter- 

 mining the general character of these clays. The worked de- 

 posits will be first discussed. 



Bordentowni. — Clay Marl I is worked in Burlington county at 

 The Bordentown Brick Company's brickyard, near Bordentown 

 (Loc. 109) . In the main pit there are 8 feet of a black sandy clay 

 of marly (glauconitic) aspect, with numerous quartz grains and 

 mica scales visible to the naked eye. The upper foot or so is 

 weathered and lean. Above the clay are 2 to 3 feet of Pensauken 

 gravel, with a similar amount of sand and more gravel. 



The black clay alone (Lab. No. 600) has a high shrinkage, and 

 cannot be used by itself, hence a clay loam is mixed with it. It 

 takes 23.4 per cent, water to> temper it, and it shrinks 8.8 per cent, 

 in drying, which is somewhat high. Its average tensile strength 

 is 251 pounds per square inch. When burned, it gives the follow- 

 ing results : 



Burning tests of a black clay, Bordentown Brick Company. 



Cone 05 01 1 3 



Fire shrinkage, 8.3% 11.8% 11.8% 11.8% 



Absorption, 10.74% 5-83% 4.01% 



Color, deep red 



Condition, not steel-hard softened beyond 



somewhat vitrification 



