CHAPTER 4. 



RAW MATERIALS IN DETAIL. 



Argillaceous Limestone : Cement Rock. 



An argillaceous limestone containing approximately 75 per 

 cent, of lime carbonate and 20 per cent, of clayey materials 

 (silica, alumina, and iron oxide), would, of course, be the ideal 

 material for use in the manufacture of Portland cement, as such 

 rock would contain within itself in the proper proportions all 

 the ingredients necessary for the manufacture of a good Port- 

 land. It would require the addition of no other material, but 

 when burnt alone would give a good cement. This ideal cement 

 material is, of course, never realized in practice, but certain de- 

 posits of argillaceous limestone approach the ideal composition 

 very closely. 



The most important of these argillaceous limestone or "ce-- 

 ment rock" deposits is, at present, that which is so extensively 

 utilized in Portland cement manufacture in the "Lehigh district" 

 of Pennsylvania and New Jersey. As this area still furnishes 

 about two^thirds of all the Portland cement manufactured in the 

 United States, its raw materials will be described in some detail 



Cement rock of the Lehigh district. The Lehigh district of 

 thie cement trade comprises parts of P>erks, Lehigh, and North- 

 ampton counties, Pennsylvania, and of Warren county, N' v '" 

 Jersey. Within this relatively small area about twenty Port- 

 land cement mills are located, producing slightly over two-thirds 

 of the entire American output. As deposits of the cement rock 

 used by these plants extend far beyond the present "Lehigh dis- 

 trict," a marked extension of the district will probably take place 

 as the needs for larger supplies of raw material becomes more 

 apparent. 



The '"'cement rock" of the Lehigh district is a highly argil- 

 laceous limestone of Trenton (Lower Silurian) age. The for- 

 mation is about 300 feet in thickness in this area. The rock is 

 a very dark gray in color and usually has a slaty fracture. In 

 composition it ranges from about 60 per cent, lime carbonate 



