MODIFIED DRIFT IN NEW HAMPSHIRE. 13 



to have been given by Dr. Edward Hitchcock in 1842* respecting a 

 series which is well shown in Lawrence and Andover, Mass. Short 

 kames, and small areas occupied by a confusion of gravel ridges and 

 mounds, but not connected with any extended series, are also frequently 

 found. 



The origin of the kames has been a question much discussed by Euro- 

 pean geologists, and the theory commonly accepted on both sides of the 

 Atlantic was, that they were heaped up in these peculiar ridges and 

 mounds through the agency of marine currents during a submergence of 

 the land. Even if such ridges could be formed by this cause under any 

 circumstances, it seemed impossible to account thus for the kames in the 

 Connecticut and Merrimack valleys, which, being bordered on both sides 

 by high hills, would have been long estuaries open to the sea only at their 

 mouths, and therefore not affected by oceanic currents. From the posi- 

 tion of these peculiar accumulations of gravel, which are overlaid by the 

 horizontally stratified drift, the date of their formation is known to be 

 between the period when the ice-sheet moved over the land and that 

 closely following, in which this more recent modified drift was deposited 

 in the open valley from the floods that were supplied by the melting ice. 

 We are thus led to an explanation of the kames, which seems to be sup- 

 ported by all the facts observed in New Hampshire, and which appears to 

 apply, also, to the similar deposits which have been described in other 

 parts of the United States and in Europe. During the melting of the 

 ice-sheet it became moulded upon the surface, by this process of destruc- 

 tion, into great basins and valleys ; and at the last the avenues by which 

 its melting waters escaped came gradually to coincide with the depres- 

 sions of our present surface. These lowest and warmest portions of the 

 land were first uncovered from the ice ; and as the melted area slowly ex- 

 tended into the continental glacier, its vast floods found their outlet at 

 the head of the advancing valley. This often took place by a single 

 channel, bordered by ice-walls, as was the case along the whole Connecti- 

 cut kame ; but in the Merrimack valley, and in eastern New Hampshire 

 and Massachusetts, these glacial rivers also frequently had their mouth by 

 numerous channels, which were separated by ridges of ice. In these 



* Transactions of the Association of American Geologists and Naturalists. 



