NEWARK ROOKS OF ROCKLAND COUNTY, N. Y. 39 



drift, which is banked up against the western side of the ridge 

 and obscures its true margin, adds an element of uncertainty to 

 these figures. At High Tor, plate 4, the crest of the ridge is 832 

 feet above the sea level, or about 530 feet (estimated) above the 

 base of the trap. But here again an unknown amount has been 

 lost by erosion, and therefore this can be taken to represent only 

 a part of the total thickness of the trap at this point. Moreover 

 the structural relations here are so indefinite that it is impossible 

 to determine with any accuracy what the maximum thickness 

 may be. 



Ladentown trap. South of the little hamlet of Ladentown and 

 almost within the shadow of Ramapo mountain, on the western 

 border of the Newark beds, there is another trap area. Its 

 greatest length is about 2 miles, measured from northeast to 

 southwest, and its maximum width is nearly a mile (fig. 9). Its 

 northwestern margin rises steeply above the valley of the 

 Mohawk creek, and is sharply marked topographically. Else- 

 where the boundary is not sharply differentiated by a change of 

 topography. Along the road leading southwest from Ladentown, 

 the trap forms a continuous ridge deeply trenched in a number of 

 places by streams. On the eastern side, also, there is a less well 

 marked ridge. Between these elevations there are a number of 

 knobs and hillocks of trap, separated by wide and deep depres- 

 sions which are encumbered with drift. 



The topography suggests that the entire area is not trap, but 

 that there are some masses of sandstone inclosed in the trap. 

 At one or two points slight confirmatory evidence was noted, 

 but the thickness of the drift is so great as to prevent positive 

 determination of this point. Within the area, therefore, marked 

 as trap there may be masses of shale, but the data in hand do not 

 warrant an attempt at separate mapping. 



Vescicular trap was noted at several points, particularly at 

 point A, figure 9, and at the northern end near Ladentown (B) 

 a ledge showed some indication of the ropy-flow structure so char- 

 acteristic of extrusive sheets. 



