MODIFIED DRIFT ALONG MERRIMACK RIVER. 9I 



being traced continuously six miles along Soucook river and fourteen 

 miles along the west side of the Merrimack, it stops here, and similar de- 

 posits were next found fourteen miles below in Hudson and Nashua. 



These kames at their beginning reach a height about loo feet above 

 the Soucook river, or 400 to 450 feet above the sea, and they continue 

 at nearly the same height above the river to its mouth, where they are 

 300 feet above the sea. Along the Merrimack they are 325 to 265 feet 

 above the sea, or 100 to 125 above the river. The only point where a 

 ridge is found much lower than this is at the eastern curve of the series, 

 in the south part of Hooksett, where it is only about 50 feet above the 

 river. The large area of kames in Manchester rises 100 feet above the 

 head of Amoskeag falls ; and the ridge and plateau south-west of Piscata- 

 quog are 15 feet lower, being 142 feet above the foot of these falls, and 

 265 feet above the sea. With an irregularity in height which is almost 

 constantly changing within limits of twenty-five feet, we thus find these 

 kames, as a series, preserving a comparatively uniform elevation above 

 the present river, which is about the same as that reached by its ancient 

 flood-plain. 



The origin of these remarkable ridges must be explained in a similar 

 manner with that of the long single kame of Connecticut river. The 

 date of their formation was at the melting of the great ice-sheet. The 

 comparatively fine gravel and frequent layers of sand in the Connecticut 

 kame attest a slow melting of the ice, long water-wearing of its material, 

 and deposition from a moderate or even gentle current. The Merrimack 

 kames, as far north as to Loudon and Concord, indicate a much more 

 rapid departure of the ice, which allowed less time for the formation of 

 rounded gravel, and was attended by strong currents. A section of the 

 Connecticut kame shows, by its alternation of coarse and fine materials, 

 that successive summers and winters were occupied in its accumulation. 

 The same appearance is often seen in the Merrimack series, but fre- 

 quently a section of these kames is without very definite stratification ; 

 and all its materials, which are then very coarse but commonly much 

 water-worn, appear to have been deposited by a nearly uniform and very 

 powerful current, like that of a single summer. 



The deep ice-channels in which the kames were accumulated seem to 

 have been formed only at or near the mouths of the glacial rivers, not 



