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MANHATTAN ISLAND
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147
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to
the friable dust, which was removed with pick and shovel. For 20 feet
to the west the surface was covered with the green actinolite dust and
fragments up to large boulders. I should say the gneiss walls were
about 4 feet apart at 128th Street, 15 feet apart at 100 feet north,
where the stump now appears. Above the present stump no solid rock
appeared on the surface, but what appeared to be a deep, green clay. On
the removal of this clay the actinolite was struck. My attention was
called to this dike almost every time I asked the men operating whether
they had found anything new. They all said it was the toughest rock
they ever had dealings with. A similar greenish soil containing
actinolite continued from the 129th Street end of the dike to the N. E.
corner of 128th Street and Convent Avenue, but I did not see solid
actinolite in place. It may have been that the actinolite was washed
down from the dike into the depression in the gneiss rock, or it may
have been that the depression was caused by the decaying of the dike in
place. The gneiss to the east of the depression was 10 to 15 feet
higher than the gneiss to the west of the depression."
East
of the degraded dike there were broad surfaces (20 feet square), rusty
brown, through iron staining, showing gneissoidal partings, which must
have been more extensive, and indicated" a possibility of slipping of
the steeply inclined foliae.
BIBLIOGRAPHY
In
1816, Hayden, in the Geological portion of Professor Cleveland's
Mineralogy, " describes a granite ridge crossing New York Island and
appearing at Hurlgate, on Long Island,thence extending into
Connecticut." (Stevens.)
Wm. Maclure, in his famous Geological Map of the United States, puts down New York Island as " primitive formation."
S.
Akerly, in 1820, published " An Essay on the Geology of the Hudson
River and the Adjacent Regions; illustrated by a geological section of
the country from the neighborhood of Sandy Hook, in N. J., northward
through the Highlands, in New York, towards the Catskill Mountains." He
speaks of the southern
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