5o 4 CLAYS AND CLAY INDUSTRY. 



just across the line in Middlesex county. It varies from 7 to 14 

 feet in thickness, is variously colored, and is overlain by several 

 feet of sand. At present it is dug by the Excelsior Terra Cotta 

 Company for use in their factory at Rocky Hill. 



Analysis of a very white clay. Isaac Webster? 



Alumina ( AU0 3 ) , 35-09 



Silica (Si0 2 ), 38.20 



Water (combined) (H 2 0), 12.10 



85.39 



Clay base — 



Silica (sand), 8.60 



Titanic acid (Ti0 2 ), 1.30 



9.90 



Fluxes — 



Potash (K 2 0), 2.44 



Magnesia (MgO), 0.21 



Ferric oxide (Fe20 3 ), 1.89 



4-54 



Total, 99-83 



Clay-working Industry. — Common brick are made at the three 

 yards as already mentioned, and terra cotta is manufactured at 

 Rocky Hill by the Excelsior Terra Cotta Company, but the clay 

 is obtained chiefly from Middlesex county, although some of it 

 is dug at pits a mile or two northeast of the works. 



1 Cook & Smock, Report upon the Clays of New Jersey, 1878, p. 232. 



