from centre to centre of middle stringers should be five feet. Intermediate cast-iron separators with bolts should be used between adjacent stringer-timbers, at distances not to exceed five feet centres.

The length of the stringer-timbers for ordinary trestles should be twenty-eight feet, so as to extend over two panels, and thus stiffen the floor system materially.

The ties should be 8" X 8" X 10'. They should be dapped over the stringers at least one-half inch and spaced thirteen inches from centre to centre.

Inside and outside guard-rails should be used for all trestles, and at each end of every trestle some satisfactory kind of rerailing device should be used. The outer guard-rail should be made of a 6" X 8" timber laid flat and dapped one inch on the ties. The inner faces of the outer guard-rails should be spaced not less than twelve inches from the gauge-planes of rails. The inner guard-rail should be 6" X 8", laid flat and dapped one inch on the ties. The outer faces of the inner guard-timbers should be placed five or six inches inside the gauge-planes of rails. Both inner and outer guard-rails should be bolted to alternate ties by three-quarter-inch bolts, which must pass through the stringers also, The heads of these bolts should be countersunk into the tops of the guard-rails by means of cup-shaped washers.

FRAMED TRESTLES.

For trestles of greater height than thirty feet, and for less heights under certain coaditions, it will be necessary to use framed bents. The foundations for these may be provided by driving piles and cutting them off above the ground, by using timber sills, or by building small masonry piers.

In all such trestles it will be necessary to brace the structure thoroughly, both transversely and longitudinally.

All framing of bents should be done in such a manner as to tie all parts firmly together.

For very high trestles it will be economical to increase the lengths of alternate panels to twenty-five or even thirty feet, and truss the stringers.