The
transportation of boulders from the north southward is an incident in
the general movement of all varieties of abraded and drifted material,
carried on the surface of the glacier, pushed slowly forward on its
edges, or still more slowly urged on beneath and in the glacier itself.
Extending over centuries, this gradual creeping southward of the comminuted and coarse rock stuff has finally culminated in a heaping up at about the
furthest limit of the ice sheet of an irregular ridge or broad chain of
hills and mounds, where the gathering deposit has reached its highest
limit. This limit has been called the " Terminal Moraine," in direct
analogy with those accumulations of earth and stones which mark the
ends of existing glaciers. It is an amazing landmark. The amount of
detrital matter embraced in this long sheet is stupendous, and when we
inspect its contents, the smoothed, water-worn or rounded stones—cobble
stones—the fine sands, pulverized rock, and imbedded boulders, the
exact conception of a continental ice mass or glacier adequate to
accomplish these results becomes difficult, and we naturally turn to
the contemporaneous picture of Greenland, buried under an " icecap,"
as a suggestive illustration.
The
" Terminal Moraine " is properly referable to the aspect of the drift
illustrated in the boulders, and it is itself the most heterogeneous
collection of transported material. It is the final outpost of the ice
sheet in its invasion of the northern hemisphere. It presents a wide
belt of interblending hills, or one long ridge with slopes more gently
declining on its southern than northern side. It reaches beyond Cape
Cod into the Atlantic, where it has been submerged beneath the ocean by
the subsidence of the land, and is traced in Nantucket, Martha's
Vineyard, Block Island, Long and Staten Islands, thence ascending to
the northwest, traversing New Jersey and so on over Pennsylvania. In
the neighborhood and within the limits of New York City it is well
developed.
The great " backbone " of Long Island is a section of this moraine, and at Jamaica and in Brooklyn its cobble-stone
