44 SURFACE GEOLOGY. 



The most important feature of this kame, if we compare it with others 

 in New Hampshire, is, that along its entire extent it constitutes a single 

 continuous ridge, which runs by a very direct course nearly in the middle 

 of the valley, having no outlying spurs, branches, parallel ridges, or scat- 

 tered hillocks of the same material associated with it. The kames in the 

 Merrimack valley and in eastern New Hampshire also average much 

 coarser, and more frequently contain angular boulders, while in some 

 places they show a gradual transition from sand and water-worn gravel 

 to unmodified moraines. 



This remarkable ridge shows the course of the glacial river by which 

 the floods from the melting ice, laden with gravel, sand, and clay, found 

 their way between ice-walls to the open valley below. All the material 

 which was thus brought down was probably gathered from the melting 

 surface of the ice-sheet ; and the pebbles were rounded in being carried 

 along by its streams. Near the mouth of the channel in which these 

 waters flowed, a portion of their gravel and sand was deposited with the 

 alternation of summer and winter. Elsewhere, kames may have been 

 formed by rivers beneath the ice-sheet; and when many boulders are 

 contained in them, or found on their surface, they seem to be most read- 

 ily explained by supposing them dropped from a melting roof of ice. It 

 is at least plain, that if any kames have been formed under the ice, they 

 must contain many boulders derived from this source. In nearly all the 

 kames of New Hampshire it seems more probable that the angular mate- 

 rials and large boulders, which we find associated with these water-worn 

 deposits, were brought by the same currents, frequently in floating masses 

 of ice. Their infrequency here puts it beyond doubt that the kame of 

 Connecticut valley was formed in an open ice-channel. It is probable 

 that this did not extend at one time over the whole distance where we 

 find the kame, but that it was gradually formed as the melting advanced 

 northward, which was at so slow a pace that for a long time walls of ice 

 enclosed the deposits of the glacial river. After these walls melted, the 

 gravel and sand remained in a long, high ridge, which became nearly 

 covered by the subsequent slow deposition of the high alluvial plain. 



When the river entered upon the work of excavating its present chan- 

 nel in the alluvium, the kame was a barrier which confined erosion to the 

 area on one of its sides and protected its opposite side ; so that this ridge 



