CLAY-BEARING FORMATIONS. 349 



were being removed. Where common brick are to be made, this 

 overlying- sand can sometimes be used to mix with the clay, but in 

 most cases it has little value except for filling. Most of the 

 Cohansey clays when freshly dug are fairly dry, and show but 

 little change in the upper layers due to weathering, because the 

 heavy overburden acts as a protective coating. 



11 'atcr for tempering. — In 28 samples tested, the water re- 

 quired for mixing ranged with one exception from 15.6 per 

 cent, to 38.2 per cent. One sample (not included in the 28), a 

 fine silty ochre from near Toms River, absorbed 65 per cent. 

 The average, leaving out this one high one, was 28.99 P er cent. 



Air shrinkage. — In such a variety of clays as the Cohansey 

 formation presents, there is considerable variation in the air 

 shrinkage, although the majority of samples show from 6 per 

 cent, to 8 per cent. The lowest was 2.5 per cent, in the sandy 

 loam from Herbertsville (Loc. 219), and the highest was 9 per 

 cent, on a clay from the Northridge property, two and one-half 

 miles southwest of Tuckerton (Loc. 211). 



Tensile strength. — With 6 exceptions, the average tensile 

 strength of all the clays tested exceeded 120 pounds per square 

 inch, 1 1 exceeded 1 50 pounds per square inch, and 3 had a tensile 

 strength of over 250 pounds per square inch. 



Burning tests. — The Cohansey clays can be divided into' two 

 groups, 1) red-burning clays, and 2) buff-burning clays. The 

 former were found at localities 191, 197, 206, 208, 211, 218 and 

 219 (see table). 



None of these burned steel-hard at cone 05, and all had to be 

 heated to at least cone 1, to reach this condition. As will be seen 

 from the tabulated tests, many samples were not tested below 

 cone 5, since on account of their being more refractory than most 

 common-brick clays, and their sandiness, they do not burn steel- 

 hard below that point. 



The buff-burning clays are found at a number of localities, 

 notably 183, 185, 195, 201, 202, 209 and 213, and many of them 

 burn to a nearly impervious body at cone 10 or 12. A few, how- 

 ever, such as those from localities 199 and 213, are porous even 

 when burned to cone 10. The clay from locality 206 contains 



