rock
and is on a hill slope, which, perhaps, has partially saved it from
reduction. It is marked by glacial contact; its smoothed and rounded
shoulders show the polishing influences of ice passing over it. But on
the southwest corner there (in Fig. 56 at the position of the human
figure) is a well-defined semicircular recess cut in the rock. This
has been formed by ice. It is a section of a pipe-like furrow which
seems shaped, rather oddly, on the side of the granite shoulder least
exposed to attack. Its character is unmistakable, and the waved crown
of the granite itself announces its experience with the abrading
agencies of ice.
In
Central Park there are many localities where these grooves appear,
while the smooth, rounded, and generally softened lens-like appearance
of the emergent swells of rock are an incontrovertible witness to ice
pressure and grinding. There are very distinct grooves on the sloping
rock at the side of the footpath below the summer house near the
Belvidere. Here, also, rock surfaces have weathered in rough, knobby,
protuberant faces from which the traces of grooves have completely
disappeared. There are grooves and broader scooped hollows on rock
domes in the Ramble. Rudely discerned wave furows, disappearing
eastward, on a much weathered rock on the hilltop above the lake, north
of the grove of Ginkgo trees. Near the granite boulders on the south
side of the " Sheep Pasture," at the walk, are two scarcely emergent
swells of gneiss well covered with scratches and broader gouges. These
are excellent and clear. West of this, on the asphalt walk, near the
West Drive, are two pared and ground surfaces of rock, full of glacial
grooves and scratches, many nearly two inches broad.
But
it is on the southern edge of the Ball Ground (lower common) that the
most magnificent examples of glaciation are to be seen. Here are broad,
deep channels on the east and a series of slanting, strongly marked,
polished and twisted grooves ascending into faces of sand-papered rock
on the west. The direction is quite deflected from the general slant of
the
