has
traced a series of beds of rock laid over these southward, and has
urged that the red gneiss, which he considers typically shown at
Yonkers, and therefore called by him Yonkers gneiss, underlies the gray gneiss of Fordham or Fordham gneiss, and that this again underlies the micaceous gneiss or schists of Manhattan Island, which latter he terms the Manhattan schist. This
view has considerable interest, and will enlist the attention of the
teachers to the fact of the varying character of these three groups of
rocks, no matter whether the inference drawn from them by Professor
Merrill is absolute or not. They will observe the more ferruginous
stained reddish gneiss on and near Jerome Avenue, a little north of the
New York City line, made up of small grains of quartz, fragments of
reddish ortho-clase and biolite, vis,, the Yonkers gneiss. Then
they may notice the Fordham gneiss (200 feet thick), which is gray,
made up of biotite and quartz, with layers of pure biotite schist and
white quartz rocks, to be met at "Fordham Heights and on 7th Avenue and
Northern Boulevard. And then the mica schist or very micaceous gneisses
of New York Island.
The
so-called Poughquag quartzite, previously mentioned (p. 7), may be
represented at Morris Docks in this borough by a very siliceous schist
(see Fig. 5), but it cannot be regarded as very significant, and its
reference to the Potsdam is certainly erroneous. Professor Berkey has
definitely sundered the Lowerre standstone from the Poughquag (north
of the Highlands), and the Lowerre and this Morris Dock film naturally
become exceptional aspects of associated gneisses, and nothing else.
An
instructive review of topographical features in the Bronx is afforded
by crossing from the Subway Elevated Railroad station at 174th Street
to the Harlem River: dark gneiss ridges are seen on 3d Avenue and
Jackson Avenue further south, with low, smoothed, abraded gneiss hills
and intermediate depressions generally declining towards the Sound and
East River, where marshy emarginations, resistant strips of rock and
islets compose an immature coast line. From
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