I04 SURFACE GEOLOGY. 



conditions which prevailed at the melting of the ice, and the modiiied 

 drift then deposited, would differ from the common type. This expecta- 

 tion was fully justified by exploration for thirty miles, along which dis- 

 tance deposits were found different from any seen elsewhere in the state, 

 together with frequent kames ; and it is only after entering Hopkinton, 

 and along the last ten miles of the river, that it is bordered by the ordi- 

 nary level and continuous alluvial plains. 



We will first describe the modified drift of this valley in order, pro- 

 ceeding from its source to its mouth, without intruding any theories ; 

 after which, we will seek an explanation of the facts observed. Several 

 ponds in the north part of Rindge constitute the head waters of Contoo- 

 cook river; and others in the same town are among the principal sources 

 of Miller's river. The water-shed on which these ponds lie is a compara- 

 tively level plateau, partly covered by large amounts of coarse, water- 

 worn gravel, and elevated i,ioo to 1,200 feet above the sea. 



At the line between Jaffrey and Peterborough, where our special exam- 

 ination of the valley began, the river is about 875 feet above the sea. 

 For the first mile the stream is bordered by coarse, water-worn gravel, 

 containing pebbles one to two feet in diameter, interstratified in nearly 

 equal proportion with sand. These deposits occur in ridges or irregular 

 terraces, which reach a height of 150 feet above the river. They are 

 well exposed by the excavations for the railroad, along which they ex- 

 tend, decreasing in height at the north, to within a half mile of Noone's 

 mill. Thence northward to Peterborough village the principal deposits 

 on the west side are sand, which slopes very irregularly from the river 

 to the height of 100 feet at the distance of a quarter of a mile on the 

 hillside. This was seen in some places to be stratified conformably to 

 the surface, and it is scarcely anywhere distinctly terraced so as to show 

 steep escarpments with a wide, level top. Boulders of various sizes, up 

 to four or five feet in diameter, are frequently found embedded in this 

 stratified sand. 



South-cast from Noone's mill we find an interesting assemblage of 

 kames, in irregular ridges, which rise from 50 to 75 feet above the river. 

 These are three or four in number, lying approximately north and south 

 and parallel to each other. Their material is water-worn gravel, contain- 

 ing pebbles up to a foot and a half in diameter. At one point a ridge 



