of grades which would have formerly been considered
prohibitive.

From the junction with the Pennsylvania Railroad, near Harrison, N. J.,
to Woodside, Long Island, a distance of 13.66 miles, there is an average
of 1.5 curves per mile; the line having a total curvature of 230
degrees. The maximum curvature is 2 degrees.

[Illustration: PLATE III.--P. T. & T. R. R. East River Division.
Sunnyside Yard]

_Method of Construction of Sub-River Tunnels._--The character of the
material through which the tunnels were to be constructed differed
greatly in the two rivers. The bed of the North River, at the level of
the tunnels, consists of silt composed principally of clay, sand, and
water, while that of the East River is formed of a great variety of
materials, such as quicksand, sand, boulders, gravel, clay, and
bed-rock. When the method of construction had to be decided there were
no thoroughly satisfactory precedents to follow in the case of either
river, although the Gas Tunnel under the East River, the partly
constructed Hudson Tunnels under the North River, the St. Clair Tunnel
under the St. Clair River, the Blackwall and several other tunnels under
the Thames River at London, supplied much useful information. The
smaller tunnels for a lighter traffic, since so successfully constructed
under the North and East Rivers, had not then been completed. Under
these circumstances, it was the desire of the Management that the Board
should receive and consider proposed methods of construction from all
available sources; and during the first year of its labors much of its
time was devoted to the examination and discussion of projects submitted
for its consideration by engineers and practical builders, some of these
projects having decided merit. Most of the methods proposed involved
temporary structures, or the use of floating plant, in the navigable
channels of the river. This was objectionable in view of the resulting
obstruction to the enormous river traffic. After full consideration of
the subject, it was decided to adopt the shield method with compressed
air for the construction of the tunnels under both rivers, this being
the only method recommended by the Chief Engineers, and having the great
advantage of conducting all operations below the bottom of the river,
thus avoiding obstruction of the channel.

Experience has shown, as was anticipated, that it is much more difficult
to construct tunnels in such material as occurs in