1879.] 229 [Upham. 
and southern portions of the district occupied by the hills here enum- 
erated, it is nearly to the south-east; but Corey’s, Parker and Bea- 
con hills, and all those which occur north-east from Boston, in the 
harbor, and in Hull, trend nearly east-south-east, even bearing in 
some cases half way between this and due east. This elongation 
seems to have been produced by the motion of the ice-sheet, under 
which these accumulations appear to have been formed. Its paral- 
lelism to the striae shows that these masses assumed their oblong 
shape because in this form they opposed the least resistance to the 
glacial current. 
There are good reasons for believing that the deflection in the 
trend of these lenticular hills was produced during the departure of 
the ice, which could hardly have its current thus deflected to the 
east-south-east at our sea-border throughout the whole glacial period. 
The southern limit of the North American ice-sheet coincided nearly 
with the course of the Columbia, Missouri and Ohio rivers. Across 
New Jersey, and on Long Island, Martha’s Vineyard and Nantucket, 
it is marked by a definite terminal moraine. The line of continu- 
ation of this is over George’s bank and the other fishing banks to the 
east-north-east. At this time, the motion of the ice-sheet, being di- 
rected toward its terminal line, was south, or between this and 
south-east over all New England. Next came a period of warmer 
climate, which drove back the ice-fields a considerable distance. 
This was followed by a cold epoch, when they again held their 
ground, and, probably after some reiidvance, preserved a nearly un- 
changed boundary through a sufficiently long time to accumulate a 
second terminal moraine, by which we are enabled to mark the vari- 
able width of the area from which they had retreated. In Wisconsin 
we find this to have been three or four hundred miles; in Ohio, about 
one hundred miles; on Long Island, and thence to Martha’s Vine- 
yard, five to fifteen miles; and at Nantucket, thirty miles. 
We are interested in this retreat of the ice-sheet in south-eastern 
Massachusetts, because it throws light upon the question when the 
lenticular hills of our district received their eastern trend. Between: 
these epochs, in which terminal moraines were formed, the ice-front 
had withdrawn from the hills in the north-west part of Martha’s 
Vineyard only five miles, to the chain of the Elizabeth Islands; but: 
its retreat from Nantucket was thirty miles, to Brewster and Orleans 
on Cape Cod. At this time we must suppose that the ice-current all 
