150 SURFACE GEOLOGY. 
about Dover, and are found frequently southward through the state. 
Isinglass, Bellamy, Oyster, and Lamprey rivers are known to be bor- 
dered in many places by intervals and low terraces and plains, but their 
modified drift has not been specially explored. 
The valley of Exeter river contains large areas of modified drift. One 
of these diverges from this river at the south-east corner of Fremont, and 
extends to the south through Kingston, Newton, and Plaistow to Haver- 
hill, Mass. This belt of modified drift reaches nearly fifteen miles, and 
is continuous from the Exeter to the Merrimack river. Along most of 
this distance it forms extensive plains. Several ponds in Kingston, which 
lie in depressions of these plains, are the sources of Powow river. 
In Newington and Portsmouth a kame-like plain of gravel and sand is 
the highest land between Great bay and the Piscataqua river; but their 
shores, with the islands of this river below Portsmouth, are almost every- 
where gently-sloping hills of till or ledge. 
Marine shells and other organic remains have been found in the lower 
portions of this valley, showing that the ocean stood at a higher level 
when the modified drift in which they occur was deposited. The more 
particular description of this district will be taken up in the same order 
as in the foregoing summary. 
Salmon Falls River. The source of this stream is East pond, which 
lies partly in Wakefield and partly in Acton, Me. It has an area of 
nearly three square miles, and a height about 500 feet above the sea, 
below which it can be drawn 18 feet, to supply the mills at Great Falls 
and Salmon Falls. This river and the Piscataqua form a part of the 
eastern boundary of New Hampshire. The descent below East pond is 
shown by the following heights, which are in feet above the sea: Horn 
pond, 479; at Milton Mills (fall), 440 to 416; at Milton Three Ponds 
dam, 412 to 400; above East Rochester, about 200; at Great Falls, 166 
to 90; at Salmon Falls, 65 to 25; at South Berwick, 20 to tide-water. 
Salmon Falls and Cochecho rivers, along their lower three miles, and the 
Piscataqua river, which is the name applied below their junction, are af- 
fected by the tide, and flow with a strong current alternately towards and 
from the sea. 
The north-west side of East pond is bordered by a low and partly 
swampy area of modified drift, which reaches a quarter to a half mile 
