The general wonder at this occurrence changed to consternation when it was seen that the glacier acted like a battering-ram of stupendous size, buckling the river ice in front of it as if ice were made of paper.  That seven-foot armor was crushed, broken into a thousand fragments, which threatened to choke the stream.  A half-mile below the bridge site the Salmon was pinched as if between two jaws; its smooth surface was rapidly turned into an indescribable jumble of up-ended cakes.

When a fortnight had passed O’Neil began to fear that this movement would go on until the channel had been closed as by a huge sliding door.  In that case the rising waters would quickly wipe out all traces of his work.  Such a crumpling and shifting of the ice had never occurred before—­at least, not within fifty years, as the alder and cottonwood growth on the east bank showed; but nothing seemed impossible, no prank too grimly grotesque for Nature to play in this solitude.  O’Neil felt that his own ingenuity was quite unequal to the task of combating this peril.  Set against forces so tremendous and arbitrary human invention seemed dwarfed to a pitiable insignificance.

Day after day he watched the progress of that white palisade; day after day he scanned the heavens for a sign of change, for out of the sky alone could come his deliverance.  Hourly tests were made at the bridge site, lest the ice should give way before the pressure from below and by moving up-stream destroy the intricate pattern of piling which was being driven to support the steelwork.  But day after day the snows continued to melt and the rain to fall.  Two rivers were now boiling past the camp, one hidden deep, the other a shallow torrent which ran upon a bed of ice.  The valley was rent by the sounds of the glacier’s snail-like progress.

Then, without apparent cause, the seasons fell into order again, the mercury dropped, the surface-water disappeared, the country was sheeted with a glittering crust over which men walked, leaving no trace of footprints.  Jackson became silent:  once again the wind blew cold from out of the funnel-mouth and the bridge-builders threshed their arms to start their blood.  But the glacier face had advanced four hundred feet from its position in August; it had narrowed the Salmon by fully one-half its width.

Fortunately, the bridge had suffered no damage as yet, and no one foresaw the effect which these altered conditions were to have.

The actual erection of steelwork was impossible during the coldest months; Parker had planned only to rush the piers, abutments, and false-work to completion so that he could take advantage of the mild spring weather preceding the break-up.  The execution of this plan was in itself an unparalleled undertaking, making it necessary to hire double crews of picked men.  Yet, as the weeks wore into months the intricate details were wrought out one by one, and preparations were completed for the great race.