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EVIDENCES OF GLACIATION 219
trap,
doubtless derived from the hill itself; others are of metamorphosed
slate, the parent beds of which probably overlie the trap on the
western slope of the hill; with these are mingled many masses of
Triassic sandstone that could only have come from the region covered by
that formation to the westward. There are also other ' erratics' in
less number composed of gneiss, quartzite, conglomerate, etc.—rocks
that are found in place only in the highlands of New Jersey, at least
thirty miles west." Fig. 61 shows a large sandstone boulder, an "
erratic," brought to the edge of the Palisades, near Englewood, N. J.
(C. J. Bates).
The drift material heaped up over lower New York on Manhattan Island has been alluded to in the accompanying1 paper
on Topography and Rocks of New York City, and in the Inwood region,
toward the Harlem, it is yet entirely evident. An interesting
statement made by Dr. Gale in relation to the beginning of 4th Avenue
can be profitably quoted: "4th Avenue commences at 14th Street, or at
Union Square. The natural soil is, in this vicinity, fifteen or twenty
feet above grading, and consists of drift, being an exceedingly
confused mass of loam and gravel (rare) and boulders of immense size.
Below grading in many places the drift loam continues some feet
downward, say six to ten, when, if we do not reach rock, we find a fine
sand, not generally white, but of dark gray, and often containing much
mica and grains of hornblende, with quartz and feldspar predominating,
and indicating that considerable portions of it had been the result of
the disintegration of granite and gneiss."
Some
years ago the superficial accumulations were removed from off the
underlying rock at 80th Street and Broadway (Boulevard), preparatory to
building. Fig. 62 shows the smoothed and ice-worn surfaces
which doubtless, before they were scoured by the ice buffer, were
irregularly weathered, pitted, and desquamate. Mr. H. Geary, one of the
engineers engaged in the work of preparing the foundations of the
Hudson Terminal building, has described to the author the dis-
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