Abbildungen der Seite

resistance to arrest in its progress the partially broken-up field. As the winter advances and the cold increases, the field of packed ice becomes stronger; and as the lakes above become frozen over, the ice from thence, which had hitherto tended so much to choke the channel, ceases to come down, and the water in the river gradually subsides, till it assumes its ordinary winter level, some twelve feet above its height in summer. The “ Ice Bridge” i. e., the complete and solid condition of the ice in the river, now becomes permanently formed for the winter, and this generally takes place about the first or second week in January. The thickest Virgin Ice seldom exceeds three feet. Upon the clear blue waters of the St. Lawrence it is perfectly transparent.

* By the middle of March the sun becomes very powerful at midday, which with the warm, heavy rains so affects the ice as to make it rotten, or as it is usually called, “ honey-combed ;” and when it is in this state, a smart blow from any sharp-pointed instrument will cause a block, even though three feet thick, to fall into thousands of pieces, as if it was composed of millions of crystallised reeds placed vertically.

* The ice, when it becomes thus weakened, is easily broken up by the winds, particularly in places where, from the great depth of water in the lakes, they do not entirely freeze over. This ice, coming down over the rapids, thickens the water, and causes a rise of the river, as in early winter. The weakened fields of ice then begin to break up, and in a few days the river becomes free, excepting upon the wharves and some particular parts of the shore, where shovings may have taken place. In these places ice may be seen for many weeks. When the lake ice comes down before that in the river and its lower basins becomes rotten, great “shovings” take place, resulting in jambs, and the consequent rise of the water-level.

* In order to avoid the dangers and difficulties consequent on these operations of nature, it was determined to build the Victoria Bridge with stone piers, placed at wide intervals, each pier being of the most substantial character, and having a large wedge-shaped cutwater of stone-work inclined against the current, and presenting an angle to the ice sufficient to separate and fracture it as it rose against the piers. The piers of the bridge were, in fact, designed to answer the double purpose of piers to carry the tubes, and of ice-breakers to encounter the pressure of the ice. In each of these respects they have fully answered the important objects sought to be attained. (P. 6.)

The site selected for the erection of the bridge is at the lower end of a small lake called the Prairie Basin, at the west end of Montreal harbour, and somewhat below the town. The river St. Lawrence is at this point 8660 feet, or a mile and three quarters, wide. Higher up, above the town of Montreal, the channel of the river is considerably narrower; and eight miles from Montreal it forms what are termed the Lachine Rapids, having a total fall of about forty-two feet in a course of two miles, but the depth of the water and the violence of the current rendered it impossible to erect piers or to face the stream in the narrower portion of its course. Opposite Montreal the river is divided into two principal channels by a large bank called the Middle Shoals ;' and although this bank is covered with boulders, which render it extremely dangerous to navigation, it afforded a useful point d'appui in the construction of a bridge designed to span the whole breadth of the river, the water being shallow at this spot except in the principal channels. Its depth at the site of the bridge varies from five to fifteen feet at summer's water level, and the bed of the stream is of limestone rock with large boulders upon its surface.

Between the quarries of Caughnawaga, whence the stone selected for the work was extracted, and the site of the bridge, the rapids of Lachine intervene, down which barges capable of carrying blocks of 100 tons weight, were driven with inconceivable force and velocity by the current. Mr. Hodges thus describes the passage of these rapids :

“The river, just above the rapids, is half a mile in width and very deep. It suddenly widens out to several miles of shallow water, tumbling over an uneven rocky bed, the whole river, as far as the eye can reach, being quite white with broken water, amidst which, in numerous places, bare rocks are visible. Through these breakers the steamboat seemed to be rushing on to destruction ; an idea which was strengthened when, after getting fairly into the rapids, the steam was shut off, and the ship was left to all appearance to her fate.

It soon, however, became evident that the vessel was passing along a deep hollow in the water, into which a torrent from either side was rushing with great velocity, without any apparent cause.

After passing along this trough for some distance the bed of the river became quite visible on both sides, within a few feet of the surface. It was now apparent that the navigable channel down which the ship was rushing was a fissure in the rock, into which the waters were pouring. At one point this chasm, only a few hundred feet in width, turned almost at right angles, and the bows of the ship approached within a very few feet of its rocky edge. The rush of waters over the sides of the channel dashed against her bows with extraordinary force; but, at the very moment her destruction seemed inevitable, she was carried round and hurried along in safety, with a wall of waters on either side of her, till the quiet lake was seen, and to our infinite relief we felt that we were safe. There is, indeed, more real danger in navigating the troubled shallow waters, filled with huge boulders, into which the river afterwards passes, than in going through the gap that looks so fearful to the inexperienced.

'It is very commonly supposed that because the steamboats pass through the most crooked part of the channel (a distance of some half mile) with the steam shut off, that all steerage way is lost. Such, however, is not the case. Care is taken that sufficient way is always left upon the ship to admit of her answering her belm. It appears pretty certain, however, that once fairly in the hollow trough formed by the chasm, a craft would pass through in safety, even though Aoating without way, like a log or raft, the rush of the water pouring into the chasm over its sides being sufficient to keep her in mid-channel.' (P. 10.)

By an ingenious adaptation of the forces of nature which periodically sway this great river, the vicissitudes of the seasons were made to assist the operations of the engineers ; and the natural obstacles to the completion of the work were not only surmounted, but literally turned into the means of bridling the St. Lawrence. In summer when the navigation was open, the torrent of its waters bore down the ponderous masses which were to be framed into the masonry of the piers. In winter when the navigation was closed, and the river itself locked in thick-ribbed ice, as firm as the rock beneath it, tracks were cut and scaffolding raised as if on dry land. But twice in each year the changes consequent on the setting in or the breaking up of the frost, necessitated a total change in the temporary works, and more than once they were exposed to destruction by the rapid alternations of the temperature.

The time chosen for the commencement of the operations was immediately after the formation of the ice bridge in January, 1854. The position of the piers and the line of the bridge was marked out on the ice, a road being hewn through the rough and thickly packed blocks, in the exact direction of the bridge itself. The sites of the piers were then marked out upon this level track by means of wooden stakes. Holes were cut in the ice round each pier, through which soundings were taken, and an iron rod was drilled into the rocky bottom to mark the centre of each of these enormous masses of masonry. During the winter crib-work moorings were also framed upon the ice, filled with stone and sunk in position above the piers. These cribs were formed of such a height that when sunk they should be about a foot above summer water level, the elevation of the ice in winter being, as we have already said, about sixteen feet higher. On this basis, soon after the spring had set in and the river was opened, the caissons for the dams were sunk, and when the dam thus formed had been pumped out, men were seen with barrows sweeping the level rock at the bottom of the river, clean of the deposit formed by a temporary leakage.

• It was a curious sight, to stand on the deck of the dam and see the waters of the St. Lawrence rush frantically past, while inside the dam the bare rock was visible with the piles resting upon it. In the

first instance not a little alarm was felt, lest something should come down the stream and displace the whole. So strong was this sensation that when a steam boat or barge came against the dam more heavily than usual, every one would be looking anxiously around, with the apprehension that some leakage might be produced by the concussion, and that those upon the dam might be compelled to seek safety in a precipitate retreat. The dam, however, stood well. By the 22nd July, the first stone was laid: and on the 14th August, the masonry (of the first pier) was above water level.' (P. 23.)

We do not propose to follow Mr. Hodges into the technical details he has given us of the construction of these extraordinary works. Those who are interested in these mechanical contrivances will find them very fully described and illustrated in this volume. But the following passage is of interest, because it relates the application of a very simple Canadian mode of building in deep water, which was found to be of the greatest utility :

It may not be out of place to say something here concerning “Cribwork,” which, although quite unknown in England, is so universally used both in Canada and the United States. The whole of the Canadian habitans use the axe with far greater facility and skill than an ordinary carpenter does in England; and, as the timber of which such work is usually constructed, flatted pine, hewn on two sides only, is very plentiful, it is constructed at little cost, and with great rapidity. Piling is comparatively little used in America, the wharves, and even the foundations for bridges in deep water being almost entirely of this “cribwork.” It is formed simply by laying timber along the whole of the outer edge of the work, and at intervals of from five to ten feet, parallel therewith throughout the whole of the breadth, connected by means of transverse timbers, firmly trenailed and notched into them. The transverse timbers for rough work are not notched down flush with the longitudinals, but are left some four or five inches up. As soon as one course of work is thus. formed, another is laid upon the top of it, and the two are firmly trenailed together. An axe and an auger are the only tools used. The flatted pine (which is usually floated in a raft to the site of the work), and a piece of freely splitting hard wood for trenails, are, with the stone required for sinking, the only materials employed. After some two or three courses are formed, it is usual to place the transverse timbers close enough together to form a flooring, upon which stone is placed to sink the crib as the work progresses. By this means the timber has never to be lifted any height till the work is above water. As soon as the underside of the crib touches the bottom it is filled with loose stone to the water level; and as in all probability the ground upon which it rests is not perfectly level, the upper course of timber work is made to correspond with the surface of the water. Above this all the courses are made perfectly fair, and to fit closely upon each other, and they are neatly chopped on VOL. CXIII. NO, CCXXIX.


the outside so as to present a smooth face, the ends of the transverse timbers being neatly dovetailed and showing upon the front of the work. Another flooring is frequently put on at the water-level, upon which the backing, if for a wharf, or the stone filling, if for a pier, rests.

The timber work below the water line, not being subject to worms, never decays; and as in the Canadian lakes and rivers the rise of the water is not great, the major part of such work is imperishable, and a stranger cannot fail to be astonished at the rapidity with which work of this description is executed, and with its stability when finished.' (P. 21.)

It has often been remarked, and never more than in the present instance, that necessity is the parent of mechanical skill, and that many an emigrant artisan who would go on at home plodding amidst all the appliances of civilisation and abundant labour, becomes a superior man when he is thrown on his own resources, and compelled to work with the scanty materials or the primitive tools of colonial life. Thus a 'steam traveller' was constructed by Mr. Chaffey, one of the sub-contractors of the bridge, of the rudest materials, and in the roughest form, but of so efficient a kind, that it moved 70,000 tons of stone twice over, performed various other duties, and remained to the end a good working engine; whilst an ingenious piece of mechanism sent out from England at a cost of several thousand pounds, for the same purpose, was thrown aside as useless.

The physical obstacles to so vast and novel an undertaking were not, however, the only difficulties with which the builders had to contend. The demand for labour in Canada and the United States was so great, that incessant strikes for wages occurred among the men ; indeed these strikes were repeated twice every year on the arrival of the spring fleet and at harvest time, to the utter disorganisation of the gangs of practical work

Added to this, the cholera broke out with frightful intensity. In one gang of two hundred men, no less than sixty were attacked at once, of whom many died. The heat of August was insufferable. Hundreds of square miles of forest took fire, and the atmosphere was loaded with clouds of lurid smoke and ashes. Moreover the works already commenced had yet to sustain the shock of the impending winter, and it was no uncommon prediction in Montreal that the first shocks of the ice would sweep away the slow and imperfect results of the year. The builders themselves lost confidence, and at that moment the work seemed almost beyond the power of man. The winter commenced in November, and early in January the hour of trial came :

The river continued to rise, and the ice to pack and shove, until


« ZurückWeiter »