When Boulder River canyon was threaded the rise to the Continental Divide commenced. The precise point at which this should be effected demanded repeated surveying, and some time passed before the engineers found the shortest and easiest path through the range. This was by means of a tunnel through the summit. A heavy piece of work was advocated--2½ miles in length--but as considerable time would be required for its completion, it was decided to take the metals right over the crests, with a temporary line of 28 miles, in order to proceed with the grade and to open up the country beyond, leaving the boring of the tunnel till a later date. Consequently, the track was carried through Rollins Pass, 11,600 feet above the level of the sea, through a world of perpetual snow. [Illustration: A DEEP CUTTING] [Illustration: [_See page 180_ BORING ONE OF THE TEN TUNNELS Cutting out the “Great Zigzag” on the New South Wales Government Railway.] To lift the line over that summit proved a tremendous task: it involved the laying out of tremendous curves and wide, sweeping loops. When built, it was quite as difficult to keep open during the winter months, when the Rockies are swept with terrific blizzards, which bury the steel highway deeply beneath hills of snow. Yet arrangements were completed to meet this emergency. A rotary snow-plough, the biggest and most powerful of its type that ever had been designed, was acquired. With this huge machine the snow-gangs were out from morning to night, but they kept that narrow channel of communication clear, though it was almost a hopeless task at times. While the railway was being pushed on from the western side of the range, the boring of the tunnel was taken in hand. It was urgent, for it reduced the summit, 2,200 feet below Rollins Pass, the portals of the tunnel being 9,930 feet above the sea on either side, rising therefrom at 1 in 400 to the tunnel’s centre line.