466 CLAYS AND CLAY INDUSTRY. 



It became steel-harcl below cone I, and vitrified between cone 

 8 and 10, but was not even semirefractory. 



The deposits of these black laminated clays are the most 

 massive found in the Raritan formation, and the only ones that 

 are large enough to permit working with a steam shovel. The 

 outlines of the pits on the map (PI. XI, Loc. 47 and 46), will 

 give a g'ood idea of the size of the excavations that have been 

 made, and Plate XXXII, Fig. 2, shows one of the banks with the 

 cars being loaded along the working face. Plate XX,, Fig, 2, shows 

 an outcrop of these clays overlain by cross-bedded sands. The 

 latter are shown in more detail in Plate I, Fig. 2. The clay is- 

 loaded on to narrow-gauge tram cars and run to- the large fire- 

 proofing and conduit factories located along the shore of the 

 Raritan river. 



A curious phase of the Raritan potter's-clay bed is found near 

 New Brunswick in the pits of the Brinckman Terra Cotta Com- 

 pany (Loc. 96). The clay rests directly on the decomposed red 

 Triassic shale, and it is difficult to> tell where one ends and the 

 other begins. The material is a fat, greasy clay, the physical- 

 properties of which are as follows : 



Pliysical tests of fireprooting clay, Brinckman Terra Cotta Co. 



Water required for tempering, 36 per cent. ; average tensile strength, i2g> 

 pounds per square inch ; air shrinkage, 7 per cent. Its behavior in burning, 

 was as follows : 



Cone 05 01 3 



Fire shrinkage, 4% 10%. 107% 



Absorption 13.12% 0.12% 0.9% 



Color, deep red red deep red 



Condition, steel-hard vitrified well vitrified 



This clay burns harder and denser at a lower cone than any 

 others used in Middlesex county for fireproofing. 



The dark laminated clays and sands are extensively worked for 

 common-brick manufacture around South River, but no samples 

 were taken for testing. They probably do not differ much in 

 their physical properties from those dug around Sayreville, and. 

 of which tests are sriven below. 



