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GEOLOGY OF NEW YORK CITY
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SERPENTINE
The
serpentine area of Manhattan Island is a very limited one in comparison
with the occurrence of this rock in Jersey-City and on Staten Island
(see Borough of Richmond), and it is mingled with calcite, forming a
blotched green and white rock known as ophio-calcite. Some
years ago I examined this locality and prepared a short paper on the
subject, from which an extract will sufficiently indicate its extent,
character and origin:
"
A bed of serpentine rock bordering the western margin of New York
Island, between 55th Street and 60th Street, and now for the most part
built over, some years ago awakened a momentary interest from its
display of strips of ophio-calcite which resembled the eozoönal (see
Dana under Laurentian) beds of Canada, and led to some surmises as to
their organic character. This area of serpentinous rock, forming a band
enclosed on the west and east by mica schists, or a highly micaceous
gneiss, and limited southward by a broad outcropping of granite, is
gradually disappearing from view and may at any time become an affair
of local record. At present its best exposure is on the north side of
59th Street between 10th and 11th Avenues, and it can be traced to near
56th Street by isolated knobs appearing above the level of the
sidewalk and in backyards. It was recently uncovered to some extent
when the cisterns for the immense gas-holders of the Equitable
Gaslight Company were being constructed, and some examinations were
then made, both of the rock in place and in microscopic sections.
"This
outcropping of serpentine is intimately associated with and
intermingles with an acicular, fibrous, partially altered hornblende or
actinolite, the hydrous anthophyllite of Dana. From this area were
derived the numerous boulders of this rock, which are found to the
south as far as the northern margin of Long Island. Dr. L. D. Gale
describes this an-
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