GRANITE
Granite is a mixture of feldspar (on Manhattan Island, orthoclase, microcline [potash
feldspar], and oligoclase [lime-soda feldspar] ), mica, and quartz,
indiscriminately combined, though in the fine-grained forms maintaining
a fairly even development.
Class Directions.—Let the teacher take some typical granite, explain its composition, separate its components, and draw attention to the contrasted arrangement of its parts, as compared with gneiss or mica-schist. Also secure specimens of varying coarseness, showing the closer admixture of the minerals in the fine-grained varieties.
The
granite on Manhattan Island reaches in one point a development
entitling it to rank as a substantial element in the island
construction, and that is on the west side from about 48th Street
northward to 55th Street, where a wide bed of it, now covered with
buildings, exists, probably at some past time attaining considerable
elevation. This granite can still be seen at 50th Street and nth Avenue
projecting from the south side of the street, a few feet west of nth
Avenue.
The
granite is of much beauty. It is irresistibly suggested that such
masses as the volume to which this may be referred were intrusive, as
the large and similar veins in the Borough of the Bronx; that they did
not originate, as the smaller conformable or cross veins of granite
did, from some re-arrangement of the gneiss in fusion, but were
actually pushed through the gneiss beds.
This
granite on the Hudson River has been used for building purposes in the
past, and the remarks made by Dr. Gale, in his report to the State
Survey, published in 1839, are of considerable interest, as indicating
its development.
He remarks " that the far greatest quantity of granite was taken from 44th to 47th Streets, near and on 10th Avenue,
