338 CLAYS AND CLAY INDUSTRY. 



terra cotta. A small amount is obtained near Woodbridge, but 

 the greatest quantity of it is dug from pits around South Amboy. 

 It is sometimes divided into No: i and No. 2 grades. 



Ball clay. — The material dug under this name conforms to the 

 usually accepted definition of the term. It is dug near South 

 Amboy (Loc. 67) and Sayreville (Loc. 273), and south of 

 Woodbridge (Loc. 29, Lab. No. 378). The clay from the first 

 two' localities is put through a washing process (PI. IX), but that 

 from the third locality is sold crude and goes under the name of 

 ware clay. 



Sagger clays are dug in many parts of the Middlesex district. 

 Their refractoriness varies from medium to low. 



Wad clay is dug at several localities. 



Terra-cotta clay. — Two types are mined in Middlesex county, 

 one a fine clay of medium or low refractoriness, and the other a 

 red-burning clay. The former kind, which is the most important, is 

 obtained from all parts of the Middlesex district, and is not al- 

 ways sold under the name of terra-cotta clay. The latter type is 

 mined west of Woodbridge. 



Pipe clays. — Most of those mined and sold under this name 

 from the Middlesex area are nonrefractory. In former years 

 sewer pipe were manufactured in New Jersey in much greater 

 quantity than they are at present, and the name pipe clay no doubt 

 originated in this manner. Certain plastic layers of dark-gray 

 clay mined around Keasbey and used in conduits are also* desig- 

 nated by this name. 



Hollow-zvare clay. — Under this term is included a great series 

 of thinly laminated black and bluish-black, sandy, micaceous clays, 

 which are found above the Woodbridge fire clay around Wood- 

 bridge, as well as along the Raritan river from Perth Amboy to 

 Keasbey and also at South River. They are extensively used for 

 the manufacture of fireproofing, hollow brick, hollow blocks, con- 

 duits and common brick. The conduits are made from the 

 smoother and more plastic beds. Some No. 2 fire clays are also 

 used in the manufacture of these hollow wares, but on the market 

 they are spoken of as No. 2 fire clays rather than as hollow-brick 

 clays. 



