120 GEOLOGY OF NEW YORK CITY
"The
physical characteristics of the North River must regulate the class of
construction which can be put there. At the Battery, rock is found at
comparatively moderate depths (less than fifty feet) below mean high
water, and the depth of the rock does not change materially below
Barclay Street. Above Barclay Street the rock becomes deeper, but
continues at a depth not far from eighty feet at the bulkhead line and
somewhat less on the pierhead line to Leroy Street. The depth then
increases. It is 124 feet at Christopher Street and nearly 200 feet at
14th Street, and these extreme depths continue to 34th Street. Above
34th Street the rock rises rapidly on the bulkhead line, but continues
very deep on the pierhead line. Over this rock is a deposit which,
though it contains in some places fairly good sand, may generally be
described as mud. It has practically no carrying capacity, and any
weight resting on its surface sinks into it at once. Any construction
built along the North River, from Barclay Street to 34th Street, must
be built in this mud. It is entirely a case of flotation. The
construction can be sustained only by making it a part of the mud.
Above 34th Street the same condition may be said to exist with the
piers, although better foundation can be found for the bulkhead wall."
If
speculation may be permitted, it seems probable that the primitive
condition of Manhattan Island, taken as inclusive of the present
water-ways, had resulted from subaerial weathering with trough and
valley creases formed by differential removal, perhaps to some extent
by faulting; that it was sculptured at a time when it was very much
above its present level, and a very moderate topographical unit in a
vastly extended primitive terrane north, east, and south, and west,
into in-selberge, irregular hillocks, longitudinal ridges with
drainage courses on the east and west. These drainage courses were
generally north and south courses. They converged on the east into the
East River, with its extension eastward over the floor of Long Island
Sound to the Housatonic and Connecticut
