GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 191 



in Massachusetts. Its length is about twenty rods ; and its height, 

 in some places, as much as fifty feet. The bank is mostly com- 

 posed of unstratified drift, from minute pebbles and sand, to 

 bowlders several feet in diameter. In the midst of the drift, occur 

 at least two quite large deposits of fine clay. The coarse drift also, 

 on the right, is stratified with a dip not less than twenty-five de- 

 grees. The upper bed of clay terminates abruptly on the right, and 

 is somewhat disturbed. It is possible that it may have been depos- 

 ited in the spot it now occupies : though in that case it must 

 have been by the agency of gentle currents of water, acting on 

 the drift that had been crowded along by the ice : but it seems 

 more probable, that the clay is a portion of some larger deposit, 

 which ^vas broken up and removed without obliterating its 

 lamination. 



Moraines constitute the great body of drift; forming ridges 

 and hills sometimes, though rarely, two hundred or three hun- 

 dred feet high. The materials are much more comminuted, and 

 the pebbles and bowlders more rounded, than the more scattered 

 drift. The most usual composition of these moraines is perfectly 

 rounded pebbles and coarse sand. In a few instances, and those 

 very remarkable, they consist entirely of sand. Large bowlders, 

 also, sometimes constitute a considerable part of the mass. But 

 in all cases there is evidence that the materials have been subject 

 to a powerful mechanical agency. 



Our moraines form ridges and hills of almost every possible 

 shape. It is not common to find straight ridges for a considerable 

 distance. But the most common and most remarkable aspect 

 assumed by these elevations, is that of a collection of tortuous 

 ridges, and rounded and even conical hills, with correspondent 

 depressions between them. These 4epressions do not form val- 

 leys, which might have been produced by running water; but 

 mere holes, not unfrequently occupied by a pond. These ridges 

 and piles form a very cm'ious landscape, and yet not strange to 

 an inhabitant of New-England. 



PI. VIII, fig. 8, represents a remarkable example of these mo- 

 raines, in the town of Truro, near the extremity of Cape Cod. 

 The hills these are composed entirely of sand, and some of them 



