to
much disturbance or a long transportation by water. The quantity was so
considerable as to defray by sale the actual expense of the contractor.
Again, on Broadway, at the corner of Ann Street, the beds of sand
excavated for the foundations, first, of the Herald building (1870), and later of the St. Paul (1896), were of remarkable depth.
Accumulations
of sand in heavy and extended beds were' encountered in Elm Street
during the construction of the Rapid Transit Subway, beds which were
continued northward through Lafayette Place, at Astor Place, through
lower 4th Avenue, and up to Union Square. Rock ledges were penetrated
beyond this point, revealing on the line, as at 23d Street, subsidences
filled with sand, clay, and surficial fillings.
Again,
on the track of the Subway beyond or north of 134th" Street very deep
hills of sand were entered, themselves partially separable by a color
line.
Seldom
in excavations of the size of that made for the new Wanamaker store has
the nature of the soil proved so advantageous to the contractors. In
the plot excavated, extending along the entire front on 4th Avenue and
back on 8th and 9th Streets about 200 feet, not one stone has been
encountered which was large enough to require a drill to dislodge it.
That
the soil generally was of clay and sand was known before actual
operations were begun, borings to a depth of 25 feet having been made
over almost the whole area. Another feature, which has greatly
facilitated the work, is the fact that at a depth of about 35 feet
below the street level there is an almost solid layer of rock. As the
depth of the foundation is to be 25 feet, it has been an easy matter to
sink the 161 caissons necessary to support the fourteen-story building
the remaining 10 feet to this solid rock.
It
has been usual to regard this assortment of beds of sand, clay and
gravel as entirely quaternary, or derived from drift. The actual
confusion of material originating in the sub-aerial erosion and
weathering of the rocks of the island, with the glacial material pushed
down over these rocks, and partially
