1879.] Jaa [Upham. 
the adjacent stratified rocks; nor is it attributable, so far as I see, to 
the contour of the land. In our district, and northward, the lentic- 
ular hills are finely developed on the low land near the coast, being 
spread over areas which would otherwise be nearly level; but at 
many places inland they are equally abundant among high irregular 
hills of ledge. They seem as likely to be found on one side or 
another of any mountain or prominent hill-range; and the altitudes 
at which they occur vary from the level of the sea to fifteen hundred 
feet above it on the height of land between the Merrimack and Con- 
necticut rivers. If their distribution has been independent of these 
conditions, as seems to be true, we are brought to the alternative 
that it probably resulted in some unexplained way from movements 
of the ice-sheet. : 
Although we do not discover the cause of the peculiar distribution 
of these hills, it seems quite certain that they were accumulated and 
moulded in their lenticular form beneath the ice, instead of being, as 
has been suggested, remnants spared by the fluviatile and tidal ero- 
sion of a once continuous sheet of drift, which was Contained in the 
ice mass and deposited at its melting. Such erosion must have 
formed table-topped hills, but ours are gracefully rounded, and their 
slopes vary from 5° to 30°, being steeper at the sides than at the 
ends; whereas erosion, as may be seen in the islands of the harbor, 
must have slopes of about 45°. Our lenticular hills, furthermore, 
are of quite variable size and height, and some which rise only fifty 
feet above the sea are as typical as neighboring ones one hundred 
and fifty to two hundred feet high. Another consideration is, that 
with such removal of equal depths of till from the spaces between 
these hills, the surface would be left literally covered with boulders 
which currents of water could not transport. 
The origin which the material and trend of these hills have been 
found to indicate, is therefore to be accepted, though some of its 
problems remain unsolved. The very hard and compact character 
of their material, the small proportion of its iron that has become 
fully oxidized, its very fine, clayey detritus, and its glaciated bould- 
ers and pebbles, all show it to be the ground-moraine of the ice-sheet, 
and the trend of its lenticular masses shows that they were shaped 
beneath the ice-current. The accumulation of these hills and slopes 
seems to have been by slow and long-continued addition of material 
to their surface, the mass remaining nearly stationary from the be- 
ginning of its deposition. Obviously this was the case with the len- 
