114 



CHAPTER III. 



OF THE MIDDLE SECONDARY ROCKS. — GEOLOGY OF THE COUNTRY BE- 

 TWEEN THE BASE OF THE HIGHLANDS AND A LINE JOINING TRENTON 

 AND NEW BRUNSWICK ; ALSO, OF THE GREEN POND MOUNTAIN. 



General Description. — In the two preceding chapters, having 

 treated in detail the geological features of the primary and the 

 lower secondary rocks, we propose in the next place to describe 

 the middle secondary strata, embraced principally within the 

 third and remaining district of the northern half of the State. 



In general aspect and composition, this group of rocks is one 

 of the most uniform and well marked in the country, and in de- 

 tailing its characters as they are beheld in New Jersey, we shall 

 be describing, in fact, the prevailing geological structure of the 

 whole belt, from the Hudson to North Carolina. 



The formation consists of dark reddish-brown sandstone, almost 

 invariably argillaceous, of soft crumbly brown shales and coarse 

 conglomerates, the latter frequently of very heterogeneous com- 

 position. The prevailing, we might say the almost invariable 

 direction of the dip of the strata is towards the north, at angles 

 varying from 15° to 25°. The lower beds, or those which show 

 themselves along the southern edge of the tract, consist most 

 frequently of rather coarse sandstones alternating with red shales, 

 the sandstones being formed of somewhat angular fragments of 

 quartz, felspar, and other ingredients of the neighbouring primary 

 rocks, cemented by a paste of brown argillaceous matter. The 

 central parts of the series consist more exclusively of brown 

 shales and brown argillaceous sandstone, while the uppermost 

 beds, occurring along the northwestern margin of the formation, 

 have frequently the character of coarse conglomerates, made up 

 of pebbles derived from a very great variety of rocks, chiefly those 

 which occur at the base or on the sides of the adjacent primary 

 hills of the Highlands. Where a large proportion of the pebbles 

 are of limestone, and the cementing red earth which unites them 

 contains an adequate quantity of the same material, the rock 



