track system are not rigidly attached to the longitudinal girders carrying the outside tracks, the central track could not be supported by supporting the outside tracks; therefore, independent supports for each track, in the form of overhead girders, had to be provided.  The columns rest on brick piers, each having four 2-in. anchor-bolts.  The brick foundations on the west side are wide in order to allow a 24-in. water main to pass directly beneath the columns.  The foundations are usually on rock.

[Illustration:  Plate XLVII, Fig. 1.—­TW 4, P.N.Y. & L.I.R.R.  Terminal Station West.  View of 9th Ave. looking Northwest from 32nd Street, prior to commencement of work.  April 23, 06.]

[Illustration:  Plate XLVII, Fig. 2.—­TW 17, P.N.Y. & L.I.R.R.  Terminal Station West.  View of East side of 9th Ave. looking North from a point 100 feet south of 33rd St. showing condition of work.  July 23, 06.]

[Illustration:  Plate XLVII, Fig. 3.—­TW 25, P.N.Y. & L.I.R.R.  Terminal Station West.  View showing permanent and temporary supports of 9th Ave.  Structures, looking Northwest from 31st.  St. April 24, 07.]

[Illustration:  Plate XLVII, Fig. 4.—­TW 28, P.T. & T.R.R.  Co.  Terminal Station West.  East side of 9th Avenue, North of 32nd St. looking West, showing rock excavation and supports of 9th Avenue structures.  Aug. 17, 07.]

Fig. 1, Plate XLVII, shows the elevated railway structure and the street surface prior to the commencement of the work.

The east track is used for north-bound local trains, the west track for south-bound local trains, and the central track for south-bound express trains between 7 and 9.30 A.M. and for north-bound express trains between 2.30 and 7 P.M.  It is said that an average of 90,000 passengers are carried over this structure every 24 hours.

Surface Railway Structure of the New York City Railway Company.—­This is an electric surface railway of the ordinary type, the rail and slot being bedded in concrete, with cast-iron yokes every 5 ft.  There are manholes every 100 ft., and cleaning-out holes every 15 ft.  Power conduits are bedded in the concrete on the east side of the east track.

Forty-eight-Inch Brick Sewer.—­This sewer was in the center of Ninth Avenue, with the invert about 12 ft. below the surface, and manholes about 100 ft. apart, and had to be abandoned in this position to allow the transverse girders to be put in place to carry all structures while the excavation was being done.

Twenty-four-Inch Cast-Iron Water Main.—­This water main was laid under the west elevated railway columns, with its top about 3 ft. below the surface, a space being left for it in the brick foundations, and a large column base casting being used to span it.  Valves were installed, one north of 33d Street and one south of 31st Street, prior to excavating near the pipe, so that if it was broken the water could be shut off promptly.