MUSEUM OF COMPARATIVE ZOOLOGY. 277 



shale." He includes this with tlie general occurrences of intrusive 

 trap. 



0. Point Pleasant Station, Belvidere Railroad, N. J. (fig. 52). — The 

 main mass of trap here seems to be a small e-xample of what is shown 

 on a larger scale farther down the Delaware about Lambertville, but 

 the smaller sheets resemble most the little outcrops at Martin's Dock, 

 and are finely shpwn. 



The first outcrops on the railroad are about five hundred feet below 

 the station, where a dark, fine grained trap shows in the bank ; it is 

 faintly columnar, but clearly bed-jointed, so that the slabs dip 12° N. 

 20° W. ; the sandstone wherever seen is closely of the same position. 

 There are no amygdules, but on some weathered surfaces the trap is 

 pitted in lines parallel to the bed-joints, showing points of chemical 

 weakness probably determined early in its history. The rock rapidly 

 becomes coarse-grained and light-colored on going northw^ard, and in 

 this form rises to the hill-top ; on the slope where seen, it is not colum- 

 nar, but breaks out in large masses and slabs ; it becomes somewhat 

 finer again, but I failed to find its northern limit, which occurs in a 

 ravine. North a little farther and opposite the station is a bed of fine- 

 grained dark trap, again showing distinct bed-joints and little cavities 

 weathered in lines parallel to its lower surface ; there is no apparent 

 cliange of structure to cause them. This trap rests on a fine, brittle 

 black slate; the junction of the two rocks is seen with few interruptions 

 for a hundred feet, and is precisely conformable to the bedding. The 

 upper surface of the trap was not seen ; but judging by the form of the 

 bank, the bed is not more than twenty feet thick. 



A little above the station there is a clifiF, thirty to fifty feet high, of 

 fine black trap ; its face is marked by joints a little steeper than a nor- 

 mal to the dip, and dividing the rock into sharp-edged columns (o) ; 

 there are other joints parallel to the bedding of the adjacent sandstone ; 

 and two four-inch bands of the same dip were traced some forty feet 

 along the face, distinguished from the rest by a peculiar roughness of 

 weathered surface dependent upon short cracks occupied by calcite. 

 This may be called a kind of vesicular structure, but not at all like the 

 ordinary trap amygdaloid. No contacts of this trap with slates were 

 seen, but the slate where found above and below was fine, black, and 

 brittle, and dipped 12° parallel to the bed-joints in the trap. 



An eighth of a mile above the station, a dry stream bed gives a 

 good series of exposures to a height of more than two hundred feet over 

 the river. Much the greater part is on fine black shale or slate, or 



