sheet
we may infer was at least 400 feet high, as high certainly as the hill.
" Such an elevation," Woodworth remarks, " of the ice-sheet increasing
northward over the sound and on the mainland would give great
hydrostatic pressure to the sub-glacial drainage, the effect of which
would be to produce violent discharge at the front in any direction,
outward or upward, in free coursing streams on the one hand, and in
fountains along the crevassed, drift-blocked ice margin on the Other
hand, in the manner of the discharge from the border of the Malaspina
glacier, as described by Russell. An overladen stream scouring the
gravelly bed of the glacier, and rising at the front through a shaft to
a point of discharge on the margin, would drop that material at the
margin in a high cone, whose ultimate form would depend on the degree
to which it was deformed by irregular deposition on buried masses of
ice, the melting of which would let down these huge kamelike heaps of
gravel in the form of mounds along the ice front."
The
two moraines unite near Roslyn, the inner crossing the outer and
continuing on into the expanding and arched elevations, on the west in
Brooklyn and at the Narrows. The moraines extend east, and are
separated by a varying interval which is 25 miles at Nantucket and Cape
Cod, 5 to 10 miles in the Vineyard sound region, 10 miles on Block
Island, with increasing convergence on Long Island. These contrasted
morainal discharges not only represent a fluctuating ice front, but a
secular modification in the main movement of ice. That is, on Long
Island, the outer moraine distinguished a more northerly and southerly
transgression of the ice, the inner, which submerges and absorbs the
outer in the vicinity of Roslyn, a more northwesterly and southeasterly
transference.
Both
were sculptured by streams; torrents emptied down their frontal
exposures; cloves or passes have been cut in them. These are noticeable
at Jamaica, Little Neck Bay, Manhasset Bay, Brookside, and East
Norwich. Reassortment of sands or clays occurred upon their southern
and northern sides, the former dipping into the broad wash plain which
sweeps seaward (15 feet to the mile) to the drowned edges
