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EVIDENCES OF GLACIATION 215
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On
8th Avenue Dr. Gale observed grooves at many points, and speaking of
58th Street, now continuously built over, he says: " Grooves are
distinct, and wonderfully so, for a diameter of two hundred or three
hundred feet, in every direction, all in fair view of the road, and on
the northeast side the grooves cover almost the whole rock, but are
most apparent on the west side, and this last remark applies equally
well to all the grooves on the island." The observation as to the
greater legibility of the grooves on the west side can be clearly
understood when it is recalled that the ice advanced from that
direction, and impinging on the island rocks, first on the west, scored
them there with their deepest impressions.
Dr.
Gale calls attention to the fact that the Manhattanville gully at 130th
Street is exactly in line with the glacial grooves. Through this pass
was pushed an ice tongue which was instrumental in collecting the
stony debris investing Harlem plain, while it wrote its signature in
furrows and scratches on the neighboring or bordering gneiss ledges. As
far east as 3d and 2d Avenues he records the grooves, and especially at
those points where in his day (1838) the rocks rose steeply, as at
Elisha Mott's quarry, about 37th Street, where the summit was sixty to
eighty feet above tide.
Although
many of all these rock surfaces mentioned by Dr. Gale have now
succumbed to the invasion of the city's progress, glacial grooves are
still easily found, and unmistakably recognized over the rock surfaces
of the island. A capital example on the very edge of the sound was
formerly visible on the shore, near Travis Island, the home of the New
York Athletic Club, east of New Rochelle. When I saw these, some ten
years ago, the earth and carpet of grass had just been removed above
them, and they appeared surprisingly fresh and distinct.
In
Bronx River Park, and over the smoothed surfaces of gneiss which are
there so conspicuous, grooves can be traced. But one example of
striated and eroded granite, near the river valley, is particularly
impressive (Fig. 56). This block of granite, raised most noticeably,
towers above the surrounding
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