143 



have enumerated all the conspicuous elevations of the trap north 

 of the Raritan river. 



Between the Raritan and the Delaware we have first the 

 Rocky Hill range, commencing, properly considered, on Law- 

 rence's brook, east of the Sand Hills, and extending across the 

 Millstone, north of Kingston, into Rocky Hill, which forms the 

 other half of this belt, to its western end. 



Almost in the prolongation of the Rocky Hill line of trap occur 

 the hills between Pennington and Woodville, and upon the Dela- 

 ware those called Smith's Hill and Bellmont. 



Northwest of Rocky Hill lies the nearly parallel range of the 

 Rock or Sourland Mountain, having the features of a broad 

 table land, rather than of a rugged dike of trap, its superficial 

 rocks being chiefly altered shales. 



Nearly in a southwestern direction from the end of the Sour- 

 land Mountain, the trap, probably of the same belt, shows itself 

 near Rocktown, ranging hence to the Delaware, where it consti- 

 tutes the bold ridge known as Goat Hill. 



Higher up the Delaware, above the mouth of the Alexsockin, 

 we find another shorter belt of trap, showing itself near the river. 



The last principal outbursts of the rock towards the northwest, 

 are the Round Valley Mountain, and the dike or dikes which 

 traverse somewhat obscurely the elevated table land styled the 

 Swamp, and which are traceable from near Black's Eddy for 

 several miles to the northeast. Several other narrower dikes 

 exist, some of which will be mentioned hereafter. 



Composition and Structure of the Trap, and its Relation to the 

 other Rocks. 



The ordinary aspect of the rock varies from that of a fine- 

 grained, compact basalt, to a coarsely crystallized greenstone 

 trap. It contains, in different localities, besides its more essential 

 components, hornblende, felspar, augite, and titaniferous oxide of 

 iron, various other minerals of more rare occurrence, such as 

 epidote, prehnite, zeolite, stilbite, analcime, and datholite. 



The rock to which we have here given the generic name of 

 trap, consists in reality of several varieties, differing somewhat in 

 composition, the more important of which it may be proper to 



