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 



