ARGILLACEOUS LIMESTONE: CEMENT ROCK. 



325 



TABLE 149. 

 ANALYSES OF HUDSON SHALE AND SLATE IN PENNSYLVANIA AND NEW JERSEY. 



* Insoluble. 



1. East Bangor, Pa. 20th Ann. Rep. U. S. Geol. Survey, pt. 6, p. 436. 



2. 1 mile northwest of Colemanville, N. J. Geology New Jersey, 1868, p. 136. 



3. Delaware Water Gap, N. J. Geology New Jersey, 1868, p. 136. 



4. Lafayette, N. J. Kept. New Jersey State Geol. for 1900, p. 74. 



though there are numerous local exceptions to this rule. The lowest 

 beds of the Hudson series, therefore, are those which outcrop along the 

 southern boundary of the formation, as above outlined. These lowest 

 beds carry much more lime and less silica, alumina, and iron than the 

 higher beds whose analyses are given in table 149.. The lowest beds 

 form a natural transition into the underlying cement rock. 



Trenton limestone. The Lehigh cement rocks, which are equivalent 

 in age to the Trenton limestone beds of New York, are made up of a 

 series of argillaceous limestones. The formation appears to vary in 

 thickness from 150 feet in New Jersey to 250 feet or even more at Naz- 

 areth and on the Lehigh River. Its upper beds near the contact with 

 the overlying Hudson shales are very shaly or slaty black limestones 

 carrying approximately 50 to 60 per cent of lime carbonate and 40 to 50 

 per cent of silica, alumina, iron, etc. Lower in the formation the per- 

 centage of lime steadily increases, while that of clayey material decreases 

 correspondingly, until near the base of the formation the rock may carry 

 from 85 to 95 per cent of lime carbonate with only 5 to 15 per cent of 

 impurities. This change in chemical composition is accompanied by a 

 change in the appearance and physical character of the rock, which grad- 

 ually loses its slaty fracture and blackish color as the percentage of lime 

 increases, until near the base of the formation it is often a fairly mas~ 

 sively bedded dark-gray limestone. Even so, it can usually be readily dis- 

 tinguished from the magnesian Kittatinny limestone, described below, for 

 the cement rock is always darker than the magnesian limestone and con- 

 tains none of the chert beds which are so common in the magnesian rock. 



The Lehigh cement rock is never nearly so high in magnesia as is 

 the underlying Kittatinny limestone. It does, however, carry con- 



