524 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



The Brunswick beds likewise change in texture toward the northeast. They are pre- 

 dominantly soft argillaceous shales from the Delaware River as far as Elizabeth. In some 

 layers an increase in coarseness is noticeable, which continues northeastward along the strike, 

 until in the vicinity of Newark and Orange the beds are chiefly sandstones. Many of these 

 beds resemble the brownstones of the Stockton series — so closely, in fact, that hand specimens 

 can be distinguished with difficulty, if at all, from much of the sandstone at Trenton and 

 Stockton. 



*^ *if l3£ ^ y^ ^ ^ ^ 



^ ^ *l* I* '*• •^ ^ ^ 



Still farther north layers of conglomerate appear interstratified with the sandstones and 

 shales. In addition to well-marked beds of conglomerate, many layers of the sandstone con- 

 tain pebbles scattered through them. The pebbles are chiefly of quartzite or sandstone, quartz, 

 slate, limestone, feldspar, and rarely of flint. Not a single gneissic or granitic pebble was 

 found, although a careful search was made for them. The coarse sandstone and conglomerates, 

 with some shale beds, continue through Bergen County, N. J., and Rockland County, N. Y. 



Beds of coarse conglomerate occur at a number of points along the northwestern border. 

 Some of these are composed chiefly of quartzite, others of limestone, and in one case of gneissic 

 and granitic material. The quartzite 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 frequently 6 or 8 inches in diameter. They are best exposed in the 

 ' 'pebble bluffs " along the Delaware River about 5 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 calcareous conglomerate is in appearance almost the exact counterpart of the famous 

 "Potomac marble" quarried at Point of Rocks, Md. The Hmestone pebbles are usually bluish 

 or gray, sometimes reddish, set in a red mud matrix, so that the rock has a variegated appear- 

 ance. The average diameter of the larger constituents is 6 or 8 inches, but bowlders 5 feet in 

 diameter have been seen, and at a quarry 2^ miles northeast of Suffern, N. Y., bowlders 12 feet 

 in diameter are reported to occur. The larger fragments are generaUy rounded, but the major- 

 ity of the smaller are sharp-cornered 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 sources of the materials, since with equal transportation the 

 softer limestones must have been most worn. 



The relations of these conglomerates to the older rocks along the border are significant of 

 faulting. In some cases the calcareous conglomerates adjoin small areas of Paleozoic limestone, 

 from which the materials may have been and probably were derived. In other cases, and 

 this is true of the largest areas, the calcareous conglomerates abut against the gneissic rocks, 

 and for much of the distance it is certain that no limestone occurs between the gneiss and con- 

 glomerate, at least not at the surface horizon. Crystalline pebbles, however, are compara- 

 tively rare in the conglomerate. SubstantiaUy the same conditions prevail in the case of the 

 quartzite conglomerate. For the most part it adjoins the gneiss, but gneissic pebbles in it are 

 rare. The known areas of quartzite along the border are small, and in general not near the 

 massive conglomerate beds. Lithologically, moreover, they are unhke the bulk of the quartzite 

 pebbles. 



It is evident that along the greater part of this border the beds of the Newark series were 

 not derived from the older rocks which now immediately adjoin them. Shore currents doubt- 

 less transported more or less material somewhat widely, and yet they do not afford us the com- 

 plete explanation for these facts. The northwestern border is for the most part marked by 

 faults. Here the dissimilarity of constitution is the most marked. Where the border is not 

 faulted and the newer rocks rest undisturbed upon the eroded edges of the older beds, they are 



