92 SURFACE GEOLOGY. 



extending far from the melting edge of the ice-sheet. In this lower por- 

 tion of the Merrimack valley, and elsewhere in eastern New Hampshire 

 and Massachusetts, the retreat of the glacier seems to have been so rapid 

 that extensions of these kames were often entirely deposited in a single 

 year. The ice-walls by which they were enclosed melted back about as 

 fast as the formation of the channels and kames advanced. Though 

 separate portions of these kames were thus probably wholly deposited 

 in a single year, their annual progress was small ; and the formation of 

 the entire series, extending 20 miles, occupied a long period. 



The substitution of coarse angular materials, instead of the common 

 water-worn gravel, seems to have taken place at times of very rapid melt- 

 ing, whenever such materials happened to be set free from the ice in large 

 amount near the mouth of the glacial rivers. They were then swept by 

 the violent current into the place of the ordinarily water-worn kames. 

 At the most notable of these localities, which occurs in Hooksett (p. 88), 

 a medial moraine, or a similar train of materials which had become en- 

 closed within the ice, seems to have been thus undermined by the glacial 

 river, and left to appear as a portion of this series. 



It remains to add a few statements in regard to kames found farther 

 southward in this valley. A fourth of a mile west from Reed's Ferry 

 we noted irregular ridges of partly angular and partly water-worn mate- 

 rials, which enclose small ponds in their hollows. These kames appear 

 to be isolated, not forming a portion of any series. After discontinuance 

 for fourteen miles next below the long series which extends from Loudon 

 to Manchester, we again find lines of kames in the main valley, upon both 

 sides of the river and a mile apart, in Hudson and Nashua. They begin 

 in Hudson, a short distance south-west of Otternic pond, and extend 

 southward two miles. This series may be seen at the north side of the 

 road leading east from Nashua bridge, near where the river road turns 

 off to the south. It is traceable from this point a half mile north- 

 ward, consisting of two or more crooked ridges 20 to 30 feet in height. 

 This material is considerably water-worn, the largest pebbles seen being 

 a foot and a half in diameter. Following the river road southward, we 

 find but a single ridge, similar in height and material, but nearly straight, 

 which lies for the first third of a mile on the east side of the road, and 

 beyond on the west side, diverging from it towards the river. This ridge 



