DETERMINATION OF LIMITS OF GLACIATION. 9 



accessible and satisfactory of these is situated one mile south of White House sta- 

 tion, in Hunterdon county. There is here a fine deposit of red till, exposed to a 

 depth of six or eight feet, containing pebbles of gneiss, quartzite, etc, from four 

 inches in diameter down, while other fragments of similar rock up to a size of two 

 and three feet are seen along the road. This deposit extends east and west, in a 

 gentle swell, for more than a mile. A trifle further southward, at Drea Hook 

 school-house, the last of the northern pebbles are seen scattered thinly over the 

 fields and quite small in size. Southward from this point for a distance of at least 

 two miles the country is entirely destitute of pebbles of every sort. The fields are 

 clean and smooth and the shale in place frequently comes close to the surface. On 

 the other hand, northward from this point for five miles through White House, 

 Potterstown and Lamington, and thence eastward through Greater Cross-roads to 

 Pluckamin, all upon the same Triassic area, there is to be found plenty of north- 

 ern material, such as Green Pond mountain conglomerates, Kittatinny mountain 

 quartzites and conglomerates, gneisses of various sorts, black flint, white quartz 

 and so on. 



Several other points in this vicinity were determined as definitely as that at 

 Drea Hook. One mile southeast of Drea Hook a similar crossing of the border 

 showed similar appearances. Still farther east the same sharp contrast occurs one 

 mile nortli of Readington, and again about two miles east of Readington. In all 

 of these cases the foreign material is distributed in such positions with reference 

 to the topography as to warrant the belief that land-ice was the distributing agent. 



Drawing a line through the points just mentioned, we find that it runs from the 

 vicinity of the junction of the northern and southern branches of Raritan river 

 with a northwesterly course to the eastern flank of the trap-ridge called Cushetunk 

 mountain. This curved ridge, rising 400 or 500 feet above the surrounding country, 

 apparently acted as a barrier against which the margin of the ice abutted, but 

 which it did not override. Northern bowlders are found plentifully around its 

 northern base, but not upon the southern. For example, in the railroad cut a mile 

 west of White House station there is a deposit of till eighteen inches deep with 

 northern pebbles up to a size of six inches. Upon examining the northern flank 

 of the ridge up to 50 or 100 feet nothing but the local trap could be detected. At the 

 town of Lebanon, on the northern base of the mountain, there is a good depth of 

 till with northern bowlders. At Annandale, two miles farther westward, there are 

 large fragments of quartzite and of Green Pond mountain conglomerate up to a 

 length of two and a half feet. On the western foot of the mountain, at Allerville, 

 four miles or more south of High Bridge, northern material is quite abundant, but 

 it disappears a short distance south of this place, and for a mile or more beyond 

 nothing foreign is found. An examination of Round valley, wliich lies within the 

 horseshoe curve of Cushetunk mountain, revealed no evidence of its having been 

 occupied by ice. 



The country west of Cushetunk mountain lies somewhat higher than that on the 

 east, and is more deeply sculptured by erosion, yet a number of points upon the 

 boundary of glaciation seemed to be satisfiictorily made out here. The underlying 

 rock is Triassic, and it would seem that all foreign materials might easily be dis- 

 tinguished in contrast with it ; but over most of the region it is the conglomeratic 

 layers of the Trias that are exposed, and which contain pebbles of northern 

 quartzites, conglomerates and probably other types of rock brought into the region 



II— Bui-L. Gkoi,. Soc. Am., Voi-. 5. 1893. 



