ORANGE AND NEWBURY SUMMITS. 65 
mainly coarse, water-worn gravel, with the largest pebbles usually about 
one foot in diameter, sometimes interstratified with considerable sand. 
Deposits which are also apparently of kame-like origin, consisting of 
gravel and sand, border the hills on the south-west side of the valley 
to East Canaan. This distance of nearly three miles has but little de- 
scent, and to the north and west the country is nearly level for consider- 
able widths in the valley, and not much lower than Orange summit. 
These areas are swampy, or are covered with low deposits of sand, which 
is also seen in patches on the hillsides from 30 to 4o feet higher. 
Large areas of low modified drift, often swampy, border the Mascomy 
river for several miles to the west. The heights of these points, in feet 
above the sea, are as follows: Grafton Centre, 871; Tewksbury pond, 
904; Orange summit, 990; top of railroad cuts, natural surface, 1,020; 
East Canaan, 956. 
The Merrimack valley, lying nearer than the Connecticut valley to the 
coast and outer limit of the great ice-sheet, and not being sheltered by a 
continuous belt of highland, was the first to become free from ice. It 
seems probable that the melting in the Merrimack basin proceeded north- 
westerly to this summit, which became the outlet from the melting ice- 
sheet over the nearly level area beyond. A long period appears to have 
followed before the ice disappeared from the Connecticut valley and along 
its bordering range of highland, of which Croydon and Moose mountains 
are the culminating points, so as at length to give the basin of Mascomy 
river a lower outlet to the west. The kames indicate the north-westerly 
retreat of the stream that descended from the glacial slopes; and the 
wide-spread, low alluvial deposits of Canaan mark the extent of the 
ancient lake, from which a large river nearly destitute of alluvium poured 
over the ledges of Orange summit into the Merrimack basin. 
Newbury summit, on the Concord & Claremont Railroad, was probably 
in a similar way the outlet from the basin of Sunapee lake during a part 
of the Champlain period. The ledge beside the highway, 150 feet east 
from the rock-cut at this summit, shows a pot-hole 24 feet in diameter, 
and the same in depth. With the present drainage no stream could exist 
to perform this work, which tells of a time when the ice-sheet had melted 
on the south-east and from the basin of Sunapee lake, while it still filled 
the valley of Sugar river, causing an outflow here to the east over the 
VOL. III. 9 
