d by transits on shore and the elevation by
measuring from the surface of the water, a tide gauge being continually
observed and the time of soundings and gauge readings kept.

In the river wash-borings were made from a floating pile-driver on which
was installed a diamond-drill outfit of rods, pump, etc. Fourteen
borings were completed in the river. Considerable difficulty was found
in holding the pile-driver against the current, the material in the
bottom being very soft, and several borings were lost owing to the
drifting of the pile-driver. Each boring was continued, and the depth of
several was more than 250 ft. below the surface of the water. The
borings on land were mostly core borings, and were generally made with
the chilled shot boring machine.

Base lines, about 2,250 ft. in length, were measured on each side of the
river, and observation points established. It was necessary to build a
triangulation tower 60 ft. high on the New Jersey side as an observation
point. The base lines were measured with 100-ft. steel tapes which were
tested repeatedly, and the work was done at night in order to obtain the
benefit of uniform temperature and freedom from traffic interruptions.
From the base line on the New Jersey side, which passed over the
Weehawken Shaft, an elevated point on the assumed center line on the
side of Bergen Hill was triangulated to, and from this point westward a
closed polygon was measured along the streets to the top of the hill on
the west side and thence along the assumed center line to the portal.
The level transfer across the river was made by sighting across in
opposite directions simultaneously, and also by tide gauges. The outline
of the final triangulation system is shown on Plate VII.

[Illustration: FIG. 2.--(Full page image)

HYDRAULIC SCREWING MACHINE WITH RATCHET DRIVE AND VERTICAL JACK

GENERAL ARRANGEMENT]

[Illustration: FIG. 3.--(Full page image)

HYDRAULIC SCREWING MACHINE WITH RATCHET DRIVE AND VERTICAL JACK

DETAILS]

The decision as to the locations of the shafts on both sides of the
river, for construction purposes and finally for permanent use, was a
comparatively simple matter, and, all circumstances considered, they are
unquestionably in the most suitable places. On the New York side the
shaft was as near as practicable to the line dividing the subaqueous
iron-lined tunnels from the land tunnels, and on the New Jersey side the
shaft was placed centrally on the line