MODIFIED DRIFT ALONG MERRIMACK RIVER. 6g 



Pemigewasset, and the name Merrimack is applied to it only from the 

 confluence of the Winnipiseogee at Franklin. * 



The modified drift of this valley in New Hampshire is illustrated by 

 Plates IV and V ; these maps, like those of the Connecticut valley, show 

 the extent of the intervals, terraces, and plains on both sides of the river, 

 with their heights above the sea. The Pemigewasset river has a develop- 

 ment of alluvium usually one half to one mile wide, which is bordered by 

 high hills or mountains, forming a deep valley similar to that of Connecti- 

 cut river along our western boundary. The modified drift of the Merri- 

 mack is usually one to two miles wide ; its greatest development is in 

 Concord, and in Litchfield and Merrimack, where it has a width of nearly 

 four miles. The hills which border this part of the valley rise with com- 

 paratively gentle slopes, and the lowest points of its eastern water-shed 

 are only 350 to 650 feet above the sea, unlike the continuous belt of high- 

 land which lies between this river and the Connecticut. After entering 

 Massachusetts the Merrimack river turns east and north-east ; and, with 

 scanty deposits of modified drift, threads its way to the sea through a 

 maze of hills which are composed of coarse glacial drift or till. Here the 

 river has no connection with the principal questions in surface geology, 

 which are quite different from those presented for study along its course 

 in New Hampshire. 



On the Pemigewasset river we find modified drift first at J. Guernsey's, 

 in Lincoln, five miles from Profile lake. Thence for two and a half miles 

 southward this consists of coarse gravel, much water-worn, extending one 

 sixth to one third of a mile in width on the west side of the river. The 

 mountains extend quite to the river along this distance on its east side. 

 This modified drift has an irregularly smoothed surface, sometimes im- 

 perfectly terraced, with its outer margin at the north from 15 to 20, and 

 at the south about 40 feet above the river. Its pebbles are from six 

 inches to a foot and a half in diameter, and sometimes larger. Boulders 

 also occur here and there, from three or four to ten feet in size. 



A large plain of similar gravel occurs east of Pemigewasset river, on 

 the north side of East Branch, having a height of from 30 to 40 feet 

 above the river. Material for this plain was brought both from the north 



*The boundaries, area, and topographic features of the Merrimack basin are described in Vol. I, pp. 205, 212, 

 300, 306, etc . 



