CLAYS OF MONMOUTH COUNTY. 473 



In making bricks from these clays the black clay is never used 

 alone, but the run of the bank is commonly taken, and to this some 

 of the sandy loam overburden is added. The sandy laminse found 

 in the clay sometimes form lenses, and it may be necessary to- dig 

 these with the clay for reasons of economy in working. 



A number of clays from, this district were tested and the results 

 are given concisely in tabulated form on page 474. In the 

 third and fourth columns there are given the physical tests of a 

 fat black clay burned alone and with the addition, of sand. The 

 addition of sand decreased the amount of water required, the air 

 shrinkage, and also the fire shrinkage. The tensile strength was 

 slightly increased and the absorption very much so-, indicating a 

 much greater porosity in the brick due to the sand. The fourth 

 and seventh columns represent soft-mud brick mixtures from 

 yards some distance apart. The sixth column (L,oc. 231) shows 

 the qualities of the weathered outcrop of a bed of Clay Marl II, 

 which is used in earthenware manufacture. It is not unlike the 

 sample of Raritan clay in the third column in most of its burning 

 qualities. 



It will also be noticed that the porosity, as measured by the 

 absorption, is quite variable in the different samples, even when 

 burned at the same temperature. Only two of the clays burn steel- 

 hard under cone 1, but all are hard enough for common brick at 

 cone 01 or even perhaps cone 03. 



Most of them have to be burned slowly and carefully to> avoid 

 cracking, swelling, or the formation of black cores. 



In actual practice it has been found that there may sometimes 

 be considerable difference in the behavior of the weathered and 

 the unweathered portions of these clays. In some cases the un- 

 weathered material may crack in drying, but this can be some- 

 times prevented by mixing in the weathered clay of the same de- 

 posit. The clay deposits of the Matawan, Cliffwood, Keyport 

 region are often sufficiently large to be dug by means of the steam 

 shovel, and where the run of the bank is to> be used, it would seem 

 to be a very profitable method of extracting the raw material. 

 Where the different layers are to be kept separate, the use of the 



