ham
gneiss, so named from the place where it is prominently developed. Near
Fordham it is a gray, narrow-banded and rather dense gneiss, at.times
very quartzose and again plentifully leaved with biotite mica, and
containing the feldspars microcline, orthoclase and oligoclase. Amongst
accessory minerals Merrill notices zircon, apatite, titanite, and
magnetite; garnet, and occasionally constituent hornblende.
This
Fordham gneiss stretches from Yonkers southward to Spuyten Duyvil, and
forms the ridges west of the Bronx. South of Spuyten Duyvil it
disappears on Manhattan Island, presumably pitching under the higher,
more loosely constructed mica-schists. It appears, however, south of
Fordham on Manhattan Island in the hill (now rapidly disappearing)
which borders 7th Avenue at 155th Street. An eastern fork "disappears
beneath the dolomite in Morrisania, but reappears near the Bronx Kills
in Mott Haven, where it forms a low, anticlinal ridge interrupted by
the kills. It was represented on Manhattan Island by a few outcrops
below high-water mark at the foot of East 1226. Street, which
are now removed. Some narrow anticlinal ridges of Fordham gneiss are
seen on the islands in the East River, notably Blackwell's, Ward's,
North Brother, and South Brother, and it is the only laminated
crystalline rock at present exposed on Long Island. There it may be
seen near the court house in Long Island City and also along the shore
of the East River from Ravenswood to Lawrence Point. It is also found
in deep well borings on northwestern Long Island, where it is the
subterrane."
The
second division of the gneiss areas embraces the Manhattan (or Hudson)
schist or the gneissoid and schistose rocks forming the surface and
underlying the surficial drift of New York Island (Manhattan Island),
and seen at Port Morris and on Randall's and Ward's Islands also.
Merrill says: "The Hudson schist is more persistently micaceous, while
the Fordham gneiss is more quartzose and more uniformly bounded. The
foliation of the Hudson is also usually morg crumpled than that of the
Fordham." This is obviously true,
