DETERMINED POINTS ON THE BOUNDARY LINE. 11 



The Altitude of the deteemixed Points. 



The altitude of the points upon this boundary line decreases from west to east. 

 Upon Musconetcong mountain it is 760 feet ; southwest of IMidvale it is 600 feet ; 

 north of Pittstown it is 460 feet ; at Sidney, 360 feet ; around the base of Cushetunk 

 mountain it is 260 feet, and at Readington, 180 feet. Further east on this line it 

 is impossible, from any observations yet made, to locate the boundary. The land 

 near the Raritan is mostly between 50 and 100 feet above tide, and although there 

 is plenty of foreign material lying upon the Triassic base, the possibility and the 

 strong probability of its having been transported by other agencies than land-ice 

 will force itself upon the mind of any observer. To the eastward and southward 

 from South Branch there is encountered at all levels up to 125 or even 140 feet 

 l^ebbles of yellow and white quartz, well rounded and about an inch in diameter. 

 They are scattered rather thinly over the fields from South Branch to New Bruns- 

 wick and from Somerville southward. On the low grounds along streams they 

 may be found gathered, with sand, to a thickness of several feet. These pebbles 

 plainly do not come from the north, but as plainly they resemble the gravel that to 

 the southeastward lies five to fifteen feet thick upon the Cretaceous belt, extending 

 from South xlmboy to Trenton. They seem to imply a submergence, accompanied 

 by water transportation from the southeast. 



Associated with these yellow pebbles in many places there are larger ones, up to 

 three inches, of white sandstone, well rounded and weathered to a buff or brown 

 exterior. True quartzite pebbles of similar appearance also occur, and, beside all 

 these, larger specimens of from 6 to 24 inches, especially of sandstones and quartz- 

 ites, are irregularly scattered over a great area from Metuchen south westward. 

 They may have been carried by floating ice. 



There is some evidence that this lobe of the ice-sheet never extended far into the 

 country south of the Raritan, on account of the barrier presented by the trap-ridges 

 called Watchung mountain or First and Second mountains. First mountain is 

 about 500 feet high and Second mountain about 600. At the base of First mountain, 

 directly north of Somerville and above the 140-foot contour, there are erratics 

 which I think were deposited by land-ice. They consist of gneiss, quartzite, con- 

 glomerate, sandstone and trap, the latter the most abundant of all. Northern 

 bowlders are also abundant at Pluckamin, on the western margin of the trap-hills, 

 but eastward of Somerville and northward of Bound Brook none of these were 

 detected ; also, careful search upon the summit of the ridge north of Somerville 

 and west of Plainfield has failed to show anything but trap. The valley between 

 the two mountains, from Washington ville to Warren ville, is likewise destitute, but 

 there is plenty of northern material from Mount Bethel to Liberty Corners at the 

 general level of 250 feet. From these facts it seems probable that the ice-sheet 

 was never sufficiently powerful to override these trap-ridges in their southernmost 

 extension, and we must look northward rather than southward for the true limit of 

 the glaciated area. 



Parallelism of glacial Boundary and Moraine. 



The glacial boundary as thus for described will naturally be compared in position 

 with that part of the moraine which lies north of it. The general parallelism of 

 the two lines is apparent. The average distance between them is about 17 miles, 



