GLACIAL DRIFT. 287 
Upper till. Lower till. 
Iron protoxide, . : i - s : 1.42 1.75 
Iron sesquioxide, . é ‘ : 3 : i 1.56 0.006 
These samples were taken within a foot of each other, close to the line 
of contact of the two deposits. The hardness of the lower till, which 
requires it to be loosened by a pick before it can be shovelled, mak- 
ing its excavation cost two to four times as much as that of the upper 
till, appears to have resulted from the immense pressure of the ice. The 
imperfect lamination, which has been commonly observed in exposures 
of the lower till in New Hampshire, may be due to the same cause, but 
more probably to its accumulation by a gradual increase of depth. It 
seems to show that the ice in its passage added new material to the sur- 
face of its ground-moraine, which generally lay undisturbed below. 
The distribution of the lower till is quite irregular, being much less 
uniform than that of the upper till, It occurs in all parts of the state, 
but is often wanting, and probably does not occupy more than half of its 
area. It is most commonly spread in flattened sheets, which may be 
nearly level, or inclined upon the flanks of hills or mountains. In the 
northern part of the state and among the White Mountains, the unmod- 
ified glacial drift often forms the slopes or rests upon the tops of the 
highest ridges. Its distribution seems to have no reference to the alti- 
tude or configuration of the land. The summits on the highland boun- 
dary between New Hampshire and the province of Quebec, as near Lake 
Magalloway and Mt. Prospect, near Third lake, are described by Mr. 
Huntington as principally covered with till. The same is true of the 
top of Moosilauke, 4811 feet above the sea. Strize show that the ice- 
sheet moved over these elevations from lower areas at the north-west, 
where a large part of its drift was probably collected, to be carried for- 
ward and deposited at a higher level. The summit of Mt. Washington 
is covered by débris (described on p. 205), which seems to correspond to 
the upper and lower divisions of the till. 
Lenticular Hills. In the south part of the state, the glacial drift is 
probably not more abundant than among the mountains, but becomes 
more interesting because of its accumulation in massive, rounded hills, 
principally composed of lower till, which form the most prominent eleva- 
tions near our coast, in Essex county, Mass., and southward to Boston.* 
* These remarkable deposits of glacial drift have been described in the Proceedings of the Boston Soctety of 
