114 SURFACE GEOLOGY. 



Rcvicxu and Conchislous. 



The continuousness in height of the plains of the Merrimack valley in 

 Concord with those through which the last ten miles of the Contoocook 

 flows, has been already noticed (p. 80). A comparison of this with the 

 deficient height of the terraces of the Merrimack opposite to and for a 

 few miles above the mouth of this river (pp. 78 and 79), leads to the 

 conclusion that a large proportion of the modified drift of Concord was 

 brought into the Merrimack valley by the Soucook and Contoocook 

 rivers. The latter contributed to the plain of East Concord, and alone 

 filled the large area between West Concord and Fisherville. 



The extensive plains of the Contoocook, in the north-west part of Con- 

 cord and through Hopkinton, occupy two basins of unequal size, which 

 we must suppose held lakes at the first retreat of the ice-sheet. These 

 were filled, as the melting of the ice continued, by the alluvium of its 

 floods. A large share was supplied by the tributaries from the north ; 

 and the kames near West Hopkinton were formed by a glacial river, 

 which descended at the head of the valley. To this point the formation 

 of modified drift seems to have proceeded quite in the ordinary way. 



In the east part of Henniker the first outlet from this valley was prob- 

 ably to the south-east into the basin of Piscataquog river. The moraine 

 and kame which extend along the old line of the New Hampshire Cen- 

 tral Railroad, at the south-west side of the alluvial area of the Contoo- 

 cook, indicate a considerable period in which the terminal front of the 

 rock-bearing glacier remained nearly stationary, succeeded by a period 

 of retreat northward, when a large river, laden with sand and gravel, 

 descended from the melting ice-fields. At the time of formation of this 

 kame a small lake, nearly as deep as to cover its top, lay between the 

 front of the glacier and the outlet of its waters to the south. The glacial 

 river, entering this deep and cjuict lakelet, deposited more quickly than 

 usual nearly its whole freight, both of gravel and sand. Somewhat later, 

 but while the outlet was still to the south, the kames on the north side 

 of the valley south-west from Whittaker pond were formed ; and we may 

 presume that this date was nearly the same with that of the kames of 

 West Hopkinton, which show that the valley of the Contoocook below 

 was clear from ice. Not long after this time the glacial barrier between 

 these basins disappeared, and drainage took its present course. Whether 



