The crossing of the Susitna includes two 121-ft. combination Howe truss flanking spans and two 70-ft. combination pony Howe truss end spans, with 392 ft. of trestle at the southern approach and 28 ft. at the northern approach, making a total length of 1,322 ft.

The spring break-up occurs usually before the ice has become soft, and in passing downstream massive pieces jam against the islands and bars and against the shore at points where the river takes a sharp turn, the water then rising until its pressure breaks the dams.

For this reason the main piers were designed to support 200-ft. steel flanking spans at some future time, each to replace the present 121-ft. and 70-ft.

Piles for the trestle bents, piers and abutments had been driven and the falsework for the steel span had been started from the north end before the track reached the site.

Excavation was started in the wet with orangepeel buckets operated by two stiff-leg derricks until hard material was struck; then the holes were pumped out and work was continued by laborers.

Several deposits along the railway line all showed the presence of this constituent in various amounts, except samples from a pit in a glacial moraine in front of Spencer Glacier, 56 miles north of Seward.

This deposit tested clear and was used; 7 per cent of sand was added to the bank aggregate, which was deficient in this respect.

A large sheet of canvas was prepared in one piece, sufficient to entirely cover the bottom area and extend about 6 ft. up the sides of the enclosure.

This canvas was "formed-in" by wooden forms along the sides and ends, to provide a runway for water around the edges.

Steam coils were placed around the sides of the pit inclosure and the entire spaced was housed in and made warm.

Sand and gravel delivered on cars were heated by being dumped on a platform holding perforated steam pipe coils, and hot water was used in mixing.

The north approach trestle, piers and falsework for timber spans were driven and a temporary deck laid.

Only a little riveting was done until after Dec. 20, 1920, when over 90 per cent of the span was in place, but the work was then pushed until completion on Feb. 9, 1921, during which time temperatures ranged from —42 to -(-34 deg.

Rivets driven during very low temperatures were retested several times later in warmer weather and showed first class work.