GLACIAL DRIFT. 309 
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. Ww. 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 inthem. 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 
