trap, granite, sandstone, and limestone (much less frequent) boulders were recorded by Dr. Gale—all northern immigrants.
It
would be wearisome to rehearse all of Dr. Gale's observations; they
repeat each other continuously, boulders of trap and sandstone brought
from the northwest in New Jersey, with no inconsiderable number torn
from higher hills on the north, on Manhattan Island itself, notably the
persistent anthophyllite (actinolite) rock.
At
present there are but few boulders known to the writer within the
limits of the Borough of the Bronx, that is, the large monolithic type
called " erratics," or " wanderers." In the Borough of the Bronx the "
rocking stone " at Bronx Park (Fig. 45) is interesting, being a large
fragment of very coarse granite about ten feet long, perhaps eight feet
wide and eight and one-half high. It resembles in texture the coarse
granites of Weschester County, and probably has not traveled a great
distance from its home to its present location. The surface on which it
stands is glaciated and smooth, and indicates to the eye its planed
and dressed condition.
In
Central Park a number of boulders of very coarse, somewhat pegmatitic,
granite can be readily found. They are beautiful themselves in their
colors and structure, the pink orthoclase, greenish plates of mica, and
projecting nodules of milky quartz forming an attractive mineral
combination. But their interest is quickly enhanced when they are
recognized as " travelers," whose vehicle of transit has been moving
ice. They are located on the borders of the " Sheep Pasture," one near
the "Mineral Springs" (sic), and a group at the south side of the same
expanse, upon and near surfaces of gneiss scratched and furrowed, most
unmistakably. These boulders vary somewhat in size, and average 8x3x5 feet in cubic dimensions, or represent each in weight nearly ten tons. (Fig. 46.)
The boulders in Brooklyn, both numerous and large, were distributed over outlying fields, protruding in shoulders out
