A discontinuous belt of dark-colored non-magnesian limestones of Ordovician age crops out along the Great Valley in New Jersey and eastern Pennsylvania. Isolated belts and patches are also infolded or infaulted in the crystalline areas of the Reading Prong. These limestones have been extensively utilized for the manufacture of Portland Cement and are frequently referred to as the “cement rock”. In 1908, Kümmel applied the name Jacksonburg to this formation in New Jersey. The Jacksonburg belt crops out discontinuously across northern New Jersey into New York State. Similar limestones are present in Pennsylvania in a continuous belt from the New Jersey border to the Lehigh River and in discontinuous belts and outlying patches from the Lehigh River to Harrisburg, where the Chambersburg limestone is first recognized.