64 SURFACE GEOLOGY. 



been blasted away. Still more remarkable evidences of water action, in 

 the form of cylindrical pot-holes, similar to those at Amoskeag and Bel- 

 lows falls, formerly existed here, but were destroyed in the work of rock- 

 excavation. The most interesting of these was called "the well ;" it was 

 situated on the north ledge, and was described by Jackson as 1 1 feet 

 deep, 4i feet in diameter at the top and 2 feet at the bottom. It was 

 originally filled with earth and round stones.* The height of the railroad 

 here is 990 feet above the sea, being about 30 feet below the natural sum- 

 mits of ledge which were thus water-worn. The south ledge was three 

 or four feet lower than the north ledge; and on both the water-worn 

 portion was at their highest points, and thence extended down their 

 south-east slopes. 



When we consider the great amount of erosion which was effected 

 during the ice age, it seems impossible that these pot-holes and evident 

 marks of extensive water-wearing could have been preserved through 

 this period, especially when we take also into account that any barrier, 

 which had before existed to turn a stream across this place, must have 

 been removed by this erosion. It becomes necessary, then, to inquire 

 how such water-wearing could be produced during the melting of the ice- 

 sheet. 



The modified drift found on both sides of this summit shows us the 

 probable answer to this question. Our examination extended from Graf- 

 ton Centre to East Canaan. The stream which we follow northward 

 nearly to Orange summit is the head of Smith's river. The first two 

 miles to near Tewksbury pond show considerable areas of low, levelly 

 stratified alluvium. From the north limit of this material we find no 

 modified drift of any consequence for about two miles, extending over the 

 summit, all the valley being ledge or glacial drift. No kame-like depos- 

 its were seen in this distance. On the north side of the north rock-cut 

 a deposit of water-worn gravel lies against the ledge. At one fourth 

 mile farther north-west we find a kame from 500 to 600 feet long and 

 about 35 feet high, the top of which has nearly the same height with 

 the top of the rock-cuts. Similar short kames, sometimes 1,000 feet 

 long, generally single, and nearly in line with each other, extend thence 

 for a mile along the south-west side of the railroad. This material is 



♦Jackson's Final Report on Geology of New Hampshire, pp. 113 and 114. 



