468 CLAYS AND CLAY INDUSTRY. 



Potash (K-0), 2.58 



Soda (NaoO), 0.80 



Water and organic matter, 8.54 



100.27 

 Total fluxes, 5.12 



This analysis shows enough ferric oxide to> make the clay burn 

 red, and sufficient total fluxes to cause the clay to fuse at a low 

 temperature. The high alkali content is due to* the abundance of 

 mica in the clay. 



II. Hollow-brick clay from the Sayre & Fisher Company's pit 

 (Loc. 71). This is also a dark-gray clay, but is much finer- 

 grained than the preceding. It took less water to work it up, viz., 

 25 per cent., and it had an air shrinkage of 6.3 per cent, with an 

 average tensile strength of 84 pounds per square inch. Its be- 

 havior in burning was as follows : 



At cone 1, it gave a red-buff body, which on longer heating 

 became red. Its fire shrinkage was 8 per cent. 



At cone 5 it was vitrified with a fire shrinkage of 10.7 per 

 cent., which is rather high. 



For use it has to be mixed with other clays. A number of firms 

 are using the above types of clay for making bricks and hollow 

 ware at Sayreville and closely surrounding localities. 



FELDSPAR. 



Southwest of Woodbridge there are several pits opened for 

 feldspar (PI. XX, Fig. 1). The general stratigraphic relations 

 of this deposit are discussed in Chapter VIII, so^ that its eco- 

 nomic characters only need to- be considered here. 



Mineralogically the "feldspar," as it is incorrectly termed, 

 is a mixture of white clay and rounded quartz grains and pebbles, 

 with a few fragments of other minerals. The material in its 

 natural condition should burn nearly white, but it is very porous, 

 and, therefore, becomes easily stained by iron oxide, which filters 

 in from the overlying glacial drift or sand beds. 



The following analyses of feldspar are taken from Prof. G. H. 

 Cook's Report on the Clays of New Jersey, 1878, p. 62 : 



