Upham.] 230 [Aprii 2, 
over eastern Massachusetts was still approximately to the south. 
The warmth of the ocean, however, had begun to melt away the ice- 
fields which encroached upon its depths more rapidly than they were 
driven back upon the land or in the shallow sounds south of New 
England. At their further departure it seems probable that this 
cause produced within the Gulf of Maine a great bay in the ter- 
minal front of the great ice-sheet, so that it was entirely melted 
away east of Massachusetts, while it yet remained in great depth 
upon all our territory except its southeast portion. The effect of this 
unequal rate of retreat would be to leave the ice upon our coast un- 
supported at its east side, and to cause its motion consequently to be 
deflected toward the vacant area. The lenticular hills were probably 
mainly accumulated before this time, having their trend in the nearly 
southward course in which the ice-sheet had hitherto moved. When 
this course was changed, it appears that these massive hills were 
turned partly around to conform to the icecurrent. This was done, 
too, in a comparatively short time, for the ice sheet was wholly 
melted before it could efface much of the previous striation upon the 
ledges, which in this same district is generally between 10° and 30° 
to the east of south. In the north-east part of Essex county and 
near the coast in New Hampshire, the old glacial markings have 
been mostly erased by the deflected ice-current, and their prevailing 
course, like that of the hills of glacial drift, is about south-east. 
The group of lenticular hills here described, has its boundary on 
the north-east, north, and north-west, at a distance of five miles from 
the State-house. In Watertown and Waltham this radius extends 
to eight miles, and continues about the same in the further circuit 
at the south-west and south, as far as to Quincy. ‘Then it increases 
to fifteen miles, reaching to Prospect Hill in Hingham and to Bear 
and Walnut Hills in Cohasset. Eastward the most remote of these 
hills are at Point Allerton and the remnant of one on Great Brews- 
ter island, both less than ten miles distant. In all parts of this dis- 
trict, with the exception of Roxbury, lenticular hills are of frequent 
occurrence. Beyond Hingham and Cohasset, massive hills, com- 
posed principally of till, but not generally of the typical lenticular 
form, extend nearly ten miles farther, to Telegraph Hill in Marshfield. 
On all other sides this area is bounded by tracts entirely destitute of 
lenticular accumulations of till, and often having scarcely any cover- 
ing upon the ledges, which are low and undulating or elevated in 
rugged and broken ranges of hills. 
