GLACIAL DRIFT. 



249 



Eagle the north and west sides, while Copp's hill on the west very nearly 

 completes the circle, with rifts for the entrance of the ice from Wildcat 

 and Ellis rivers. On nearly every side the material low down consists 

 of an immense thickness of till, cut deeply by small streams. This de- 

 posit gives an evenness of slope to the hills about Jackson that is uncom- 

 mon among the mountains. It is believed that the till is mainly of 

 ancient glacial origin brought from the north-west, and that the latest 

 ice movement smoothed it over and left many large blocks of stone and 

 small moraines. The north slope of Pickett hill shows several examples 

 of what appear to be local moraines. Packard speaks of a block of 

 many tons' weight upon a hill near Goodrich falls brought in this way 

 only a few rods. In the neighborhood are striae pointing S. 17° W., as 

 if connected with the valley movement just mentioned down the tribu- 

 tary of the Wildcat river.* 



Pot-holes. In northern New England there are many examples of pot- 

 holes worn in ledges far away from existing streams. These are believed 

 to have been formed by currents of water derived from the melting ice- 

 sheet, passing down the crevasses of the glacier. Those on the summit 

 between different valleys were formerly referred to the agency of one of 

 the rivers pouring over the divide into the other depression. Many of 

 our examples are so situated that such a theory would not explain them, 

 I append a list of the principal pot-holes that have come to my notice : 



One 4 feet deep on top of Svvett's mountain, Gilmanton. 



One of large size in Wentworth. It is on tlie south-west side of Carr's mountain, 

 from 300 to 500 feet above Baker's river. 



In the "Flume," Dixville, I saw one, 4 feet in diameter and 7 feet deep, in the pro- 

 cess of formation. 



On a ledge exposed for 200 feet, near its south end, a conical one, 2 feet in diameter 

 at the top, and about 2 feet deep. It is 125 feet above the river at East Weare, and in 

 the edge of Dunbarton. It is called " Indian mortar" by the people living in the neigh- 

 borhood. 



The same name is applied to a pot-hole near the top of Beech hill in New Hampton, 

 about 600 feet above the valley of Lake Wukawan. It is situated on the south-western 

 peak, not quite so high as the other, and perhaps 15 rods south of and 40 feet lower 

 than the highest point. There are no other evidences of vrater action on the ledges of 



* I have assumed that Packard's observations were not corrected for the variation of the compass, as he does 

 not say anything about it. 



