324 CEMENTS, LIMES, AND PLASTERS. 



Cement Rock of the Lehigh District, Pennsyivania-New Jersey. 



The "Lehigh district" of the cement manufacturer has been so 

 greatly extended in recent years that the name is now hardly appli- 

 cable. Originally it included merely an area about 4 miles square, 

 located along the Lehigh River partly in Lehigh County and partly in 

 Northampton County, and containing the villages of Egypt, Coplay, 

 Northampton, Whitehall, and Siegfried. The cement-plants which were 

 early located here secured control of most of the cement-rock deposits in 

 the vicinity, and plants of later establishment have therefore been forced 

 to locate farther away from the original center of the district. At 

 present the district includes parts of Berks, Lehigh, and Northampton 

 Counties, Pa., and Warren County, N. J., reaching from near Reading, 

 Pa., at the southwest, to a few miles north of Stewartsville, N. J., at the 

 northeast. It forms an oblong area about 25 miles in length from 

 southwest to northeast and about 4 miles in width. Within this area 

 about twenty Portland-cement plants are now in operation, and the 

 Portland cement produced in this relatively small district amounts to 

 over half of the entire United States output. 



Geology of the district. Within the " Lehigh district" three geo- 

 logic formations occur, all of which must be considered in attempting to 

 account for the distribution of the cement materials used here. These 

 three formations are, in descending order, the (1) Hudson shales, slates, 

 and sandstones; (2) Trenton limestone (Lehigh cement rock); (3) Kitta- 

 tinny limestone (magnesian). As all these rocks dip, in general, north- 

 westward, the Hudson rocks occupy the northwestern portion of the 

 district, w r hile the cement rock and magnesian limestone outcrop in 

 succession farther southeast. 



Hudson shale. This series includes very thick beds of dark-gray 

 to black shales, with occasional thin beds of sandstone. In certain 

 localities, as near Slatington and Bangor, Pa., and Newton, N. J., these 

 shales have been so altered by pressure as to become slates, the quarry- 

 ing of which now supports a large roofing-slate industry. 



The composition of the typical shales and slates of the Hudson for- 

 mation is well shown by the following analyses (Table 149). 



The geographic distribution of the Hudson shales and slates in the 

 Lehigh district can be indicated only approximately without the pres- 

 entation of a geologic map of the area. They cover practically all of 

 Northampton, Lehigh, and Berks counties north of a line passing 

 through Martins Creek, Nazareth, Bath, Whitehall, Ironton, Guthsville, 

 Monterey, Kutztown, Molltown, and Leesport. 



The rocks of the Lehigh district have a general dip to the northwest, 



