118 SURFACE GEOLOGY. 
through Greenfield. The last blockade of the ice-shect in its retreat to 
the north may have been at Long fall, in the west part of Henniker, 
where the high hills leave a narrower space than usual for the passage 
of the river. The large proportion of sand in the kames of the north 
part of Bennington is what we should expect, if their deposition was at 
the mouth of glacial rivers where they entered the lake. The most im- 
portant testimony, however, is given by high deposits of sand and fine 
gravel, like that on Hedgehog hill in Deering. The widened lake now 
filled the whole valley; and these deltas, brought in by glacial rivers or 
tributary streams, mark its height and shore line, and enable us to gauge 
the floods which were supplied from the melting ice. 
The earliest of these lake-shore deposits are the plain of Greenfield 
and that of Hancock village. Both of these have the same height 
with the outlet, over which there as yet flowed only a shallow stream. 
When the lake had advanced north to Clinton village in Antrim, the 
depth of its outflow was probably 20 feet, as shown by a level-topped 
ridge of sand and fine gravel exposed on the north side of Great brook 
and the road, a quarter of a mile east from Hastings’s mill. This deposit 
extends a quarter of a mile to the north, and also occurs south of this 
stream, by which it was formed about at the level of the lake. High 
sand was also found three miles farther north, on the water-shed between 
Cochran brook and North Branch, at the south-west side of Riley moun- 
tain. This is two and a half miles due west from that on Hedgehog 
hill. Both these deposits are level-topped deltas of glacial streams that 
descended to the lake from the north, having the place of their inlet de- 
termined by the gap of the adjacent hills. Their heights are the same, 
and show that at the time of their formation 50 feet of water poured 
over the outlet in Greenfield. Somewhat later, when the lake reached 
its greatest extent and received its largest tribute from the more rapidly 
melting ice-sheet, the depth of water discharged was 80 feet, as shown 
by a delta-terrace half a mile south-west from Hillsborough Centre, and 
by plains which occur at the same height north-east of Hillsborough Up- 
per Village. All these deposits are level-topped, or nearly so; and their 
position is generally on steep hillsides, with no barrier, if the drainage 
had been the same as now, to prevent their being carried forward to the 
bottom of the valley. Other deltas similar to these might probably be 
found by a more thorough exploration of the ancient lake shore. 
