146 SURFACE GEOLOGY. 
the level of Ossipee lake, which is 408 feet above the sea. In their west- 
ern portion they are from 40 to 50 feet above Bear Camp river, which 
along its last six miles flows through fertile intervals. These cover areas 
from which the river has excavated the higher plain. The upper part of 
this river is also frequently bordered by intervals and terraces. 
The shores of Ossipee lake are mostly low; and it appears that this 
area remains unfilled because sufficient material has not been supplied by 
inflowing streams. We cannot thus explain the unfilled hollows of Six- 
mile pond, and of Elliot and White ponds in Tamworth; for the level 
plain adjoining them is from 25 to 40 feet in height, and descends steeply 
to their shores. Probably masses of ice filled these depressions while 
the bordering plains were being deposited. 
Till extends in a gentle slope to the margin of Ossipee lake along a 
distance of about a half mile on its north-east side. Barren pine-plains 
reach thence for three miles to the east. These are divided by the irreg- 
ular chain of Danforth ponds, which have the same height with the lake. 
At Danforth bridge these plains are nearly level, and have a height of 
35 feet above the ponds, to which they descend in steep escarpments., 
Their material is mainly sand or fine gravel; but coarse gravel, con- 
taining pebbles from six inches to one foot in diameter, is occasionally 
found, and appears to belong to kames which have been nearly buried 
beneath the fine alluvium. 
Ossipee river, the outlet of this lake, flows over till at Effingham falls, 
and along its last mile before entering Maine. In the intervening three 
miles it is bordered by low modified drift, which extends to Swasey pond 
in Freedom, and forms an extensive tamarack swamp in the north-east 
corner of Effingham. 
On the west and south sides of Ossipee lake the modified drift is one 
half mile to a mile and a half wide. Its highest portion is a delta-plain on 
the north side of Lovell’s river, 40 feet above the lake. Elsewhere it is 
low, being swampy in many places, and rises only 15 to 25 feet above the 
lake, towards which it slopes. 
These nearly level areas are bounded by hills and mountains, which 
rise steeply from the edge of the plains. The supply of modified drift 
was very abundant here, and fills three fourths of the natural lake-basin 
which is thus enclosed. 
