THE NEWARK ROCKS 33 



conglomerate contains a few pebbles of limestone, shale, and 

 gneiss, but almost the entire mass of the rock is made up of 

 quartzite or sandstone pebbles, which are well rounded and fre- 

 quently six or eight inches in diameter. They are best exposed 

 in the "pebble bluffs" along the Delaware River about five miles 

 above Frenchtown. The conglomerates are interstratified with 

 sandstones and shales, forming lenticular beds, which thin out 

 within a few rods, to be replaced by beds of a different texture. 

 This alternation and rapid change betoken shore conditions. 

 The quartzite conglomerate is also well developed (<?) in "the 

 Barrens" northwest of Pittstown, {Ji) south of Clinton, (V) four 

 miles north of Peapack, where there is an outlier called Mount 

 Paul, (d) south of Morristown, and (e) south of Pompton Lake. 



The calcareous conglomerate is in appearance almost the 

 exact counterpart of the famous " Potomac marble " quarried at 

 Point of Rocks, Maryland. 1 The limestone pebbles are usually 

 bluish or gray, sometimes reddish, set in a red mud matrix, so 

 that the rock has a variegated appearance. The average diame- 

 ter of the larger constituents is six or eight inches, but bowlders 

 five feet in diameter have been seen, and at a quarry two and a 

 half miles northeast of Suffern, N. Y., bowlders twelve feet in 

 diameter are reported to occur. The larger fragments are gen- 

 erally rounded, but the majority of the smaller are sharp-cor- 

 nered or at most subangular. Compared with the pebbles in the 

 quartzite conglomerate, the limestone pebbles are but little worn, 

 a fact of some significance in connection with the origin and 

 source of the materials, since with equal transportation the softer 

 limestones must have been most worn. In many localities this 

 conglomerate is so pure a limestone that it is quarried and burnt 

 for lime for local use. 



Three small areas of this conglomerate occur northwest of 

 Pittstown between hills of the quartzite conglomerate. A much 

 larger area lies along the border northwest of White House. In 

 New York state it occurs (#) two to three miles northeast of 

 Suffern, (b) near Ladentown, and (V) south of Stony Point. 



'Geological Survey of Maryland, Vol. II, pp. 187-193. 



