Serpentine
has been found in connection with the dolomite of the island, as at
Lexington Avenue and 123d Street. An-thophyllite and actinolite
boulders have been found southeast of the 59th Street locality, at
Corlear's Hook and on Long Island.
It
is altogether probable that a short range of low hills having some
genetic connection with those of Hoboken once occupied a part of the
western margin of Manhattan Island at about 59th Street; that they have
been chiseled away; that for some reason they were especially
vulnerable to the attacks of the ice sheet, and that their eroded
foundations have now only the single visible witness in the low mound
near nth Avenue. Dana regards this serpentine locality as related to
the limestone areas in Westchester County, in which serpentine is known
to occur. The name ophio-calcite, applied to some of these
ser-pentinized rocks, is, in strictness, inaccurate. A true
ophio-calcite consists of an original limestone in which amphibole or
pyroxene has changed to serpentine. In the 58th Street rock the calcite
is secondary, being a chemical deposit formed in the process of an
original amphibole changing to serpentine. In both cases the physical
results resemble each other.
Dr.
Julien visited this locality in West Fifty-fourth to Sixty-third
Streets,as early as 1878, and his observations, in field notes,
indicate " a basin-like depression, with swampy bottom and deeply
gullied sides about Fifty-eighth Street, which seemed to have been excavated
in the softer material during some ancient time by a small stream
running westward to the [Hudson." His allusions to the serpentine
appear to be included in these words: " Blackish-green, tremolitic,
serpentine !(spotted with greenish-gray altered actinolite), about 40
feet, inclosing thin sheets of tremolite schist; hydrated tremolite:
schist (hydrous-anthophyllite) at least 60 feet, inclosing many layers
and amorphous masses of serpentine, ophio-calcite, compact tremolite
rock, and sometimes asbestus."
M. A. Yeshilian assures me that boulders of asbestus and
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