208 CLAYS AND CLAY INDUSTRY. 



by the solution and removal of the calcium carbonate. It is used in 

 the manufacture of common brick. 



Outside of the moraine the shale also is deeply weathered, as 

 is well shown in several railroad cuts between Hackettstown and 

 Washington. At Port Murray (Loc. 282) it is utilized by the 

 Natural Fireproofing Company in the manufacture of fire- 

 proofing (Plate LVI). Similar weathered material occurs abun- 

 dantly in this vicinity and in the shale belt west of Clinton along 

 the line of the Central R. R. of New Jersey. 



North of the moraine the shale is covered by the glacial 

 drift, or if exposed, is in general but slightly weathered. The 

 fresh shale, when ground up and mixed with water, is lacking 

 in plasticity and tensile strength and, therefore, does not give such 

 good results as that which has been deeply weathered. This being 

 so, it is doubtful whether the great shale deposits within the 

 glacial area will ever prove of value for these purposes. 



PRE-CAMBRIAN ROCKS. 



The pre-Cambrian rocks occur in the Highlands. They are 

 chiefly gneisses, schists and granites. Some of the latter are 

 coarse feldspathic rocks, although by far the greater part are not. 

 Under favorable conditions the decay of a coarse-grained granite 

 will give rise to a mass of kaolin, with some mica and quartz. 

 Such deposits are known to occur in New Jersey, but they are 

 of small extent and unworked at the present time. 



In the Annual Report for 1874 such a deposit is noted as 

 occurring in a narrow valley one and one-half miles southwest 

 of Bethlehem, Hunterdon county, on lands owned by Mr. Will- 

 ever, and later by S. L. Shimer, of Phillipsburg. A shaft 33 feet 

 deep is reported to have been sunk in it without reaching its 

 bottom. The bed was a mixture of white clay, with a large per- 

 centage of very fine white quartz and partially decomposed feld- 

 spar. Analyses of the crude material show a large amount of 

 potash, with some lime and magnesia and a little oxide of iron, 

 the latter giving it a dark color in burning. 



