the Manhattan side, and temporary transit stations were established on
buildings from which all borings in the river were located. The river
borings were all wash-borings made from a pile-driver boat. After the
results were plotted on the map, contour lines were drawn to indicate
the rock surface, and profiles along the tunnel lines were plotted from
the contours; as the borings were preliminary to the final location of
the tunnels, and in many cases at some distance from the tunnel lines,
considerable divergence from the actual rock surface was expected, and
realized in a few places, yet on the whole the agreement was very good.
The borings revealed two depressions or channels where the rock surface
passed below the grade of the projected tunnels, these depressions being
separated by a rock reef which extends down stream from Blackwell's
Island. In 32d and 33d Streets in Manhattan, borings were made from the
river to the station site at intervals of about 100 ft., wash-borings
and core-borings alternating. In Long Island City, where the tunnel
lines were to pass diagonally under the passenger station building and
passenger yard of the Long Island Railroad and under streets and private
property, the arrangement of borings was less regular, although the
alternation of wash-borings and core-borings was carried out as far as
practicable. After the final location of the work, additional borings
were made, particularly on shaft sites and also along the approaches and
in the Sunnyside Yard, Long Island City.

A triangulation was carried across the river with a measured base on
each side. It was impossible to measure directly between the extremities
of either base. The bases were measured with 100-ft. steel tapes,
supported every 20 ft., stretched with a uniform pull, and frequently
compared with standardized tapes. On account of the crowded condition of
the streets during the hours of daylight and evening, most of the work
was done between 10 P. M. and 5 A. M. Similar measurements were made in