ward
and escape to the ocean through a demonstrably deep channel between
Plum and Fisher's islands and Montauk Point and Block Island. Then also
the filled-up north shore valleys of the island were re-excavated. It
was a long interval of erosion.
The
Wisconsin Stage preceded the Recent, and left the wholly remarkable
testimony of its work in the great moraines that cross Long Island from
end to end and also cross each other. These long mounds, heaped upon
previous deposits, whose hidden saliency causes them to appear more
voluminous than they really are, have at points on Long Island a height
above tide of 400 feet. The Wisconsin moraine has given to Brooklyn its
higher elevations in Prospect Park, Greenwood Cemetery, the ridge at
Bay Ridge, and at Fort Hamilton, though from 192 feet at Ridgewood,
Brooklyn, it thins away to a few feet at Babylon. It is distinguished
by large erratics.
The Wisconsin moraine is typical boulder till, unstratified drift, and reworked drift, vis., more
or less stratified. It is an accumulation at the edge or near the front
of the ice sheet, so far as it is a terminal moraine; beds formed under
the ice sheet or ground moraines; and frontal wash plains, deltas, and
kettles. The frontal wash plains have arisen from the drainage from
the glacier, reassorting and separating mechanically transported
burdens of sand and clay and influenced by wave action from the sea;
the deltas are fan-shaped deposits left by spreading streams from
higher points; and the kettles are holes or funnel-like depressions
left by melting ice masses, whose included mineral contents or loads
heap up around their positions a wall of debris, which may finally
frame a pond or lakelet. The two moraines alluded to are shown in Fig.
38, fom Veatch's monograph; the more southern, passing through the
Montauk arm (South Fluke) of Long Island, is prolonged eastward over
Block Island, Martha's Vineyard, and Nantucket. This marks the
Ronkonkoma stage of the ice sheet. The inner and northern which crosses
the southern moraine towards the west, and delimits the eastern edge of
the harbor
