GLACIAL DRIFT. 3O9 



ploughed up by the enormous pressure of the ice passing over it. How 

 could this force permit the ground-moraine to be heaped in the steeply- 

 projecting lenticular hills ? Instead of this we should expect it to be 

 left only in flattened sheets or behind sheltering ledges. The probable 

 answer seems to be, that the finely pulverized detritus and glaciated 

 stones in the bottom of the ice-sheet had a tendency to lodge upon the 

 surface of any deposit of the same material. When such banks of the 

 lower till became prominent obstacles to the ice-current, its levelling 

 force was less powerful than this tendency of adhesion, which continually 

 gathered new material, building up these massive rounded hills. At 

 the melting of the overlying ice-sheet, the surface of hills and valleys, 

 ground-moraine and ledges, were alike covered by the nearly continuous 

 mantle of the upper till. w. u. 



Note upon Lenticular Hills, by C. H. Hitchcock. 



Thorough search for these moraines has been made in all parts of the state south of 

 the White Mountains, not including Grafton county. Not many more will be added 

 by future observations. I do not think any occur in Grafton county. In Canaan, long 

 drift covered hills south of the centre bear some resemblance to them. A trip through 

 eastern Vermont revealed facts of interest. In Orange two hills in the south-west 

 corner resemble lenticulars, and, as seen from a distance, there appear to be genuine 

 examples on the north-west side of the church. In Peacham and Danville, num- 

 erous rounded hills resembling these moraines may be seen from elevated positions. 

 Some that I examined proved to be composed of limestone, weathered roundish; so 

 it seems probable that all the others are similarly constituted. One not familiar with 

 the behavior of this rock, when acted upon by atmospheric agencies, might call all 

 these mounds lenticular hills. Large drift hills are known to occur in Bethlehem and 

 Whitefield. Another trip to the localities would be requisite to enable me to pro- 

 nounce upon their existence in these towns or elsewhere in Coos county. It seems 

 probable that the great drift hill just west of Chocorua pond in Tamworth should be 

 of this character. The heliotype illustration of some of these hills in Goffstown ad- 

 mirably represents their general character. All the hills in the view are true lenticular 

 ground-moraines, with no ledges in them. They are simply piles of earth and stones 

 accumulated beneath the ice-sheet, and afterwards covered by the upper till. The 

 information contained in Mr. Upham's description of these hills is one of the most 

 valuable contributions to science obtained during our whole survey of the state. 

 VOL. III. 40 



