Изображения страниц

180 CHAT MOSS. Chap. XI.

parts where the moss is the deepest. This occurs through the capillary attraction of the fibres of the submerged moss, which is from twenty to thirty feet in depth, whilst the growing plants effectually check evaporation from the surface. This peculiar character of the Moss has presented an insuperable difficulty in the way of draining it by any system of wholesale drainage—such as by sinking shafts in its substance, and pumping up the water by steam power, as has been proposed by some engineers. Supposing a shaft of thirty feet deep to be sunk, it has been calculated that this would only be effectual for draining a circle of about one hundred yards, the water running down an incline of about 5 to 1 ; for it was found in the course of draining the bog, that a ditch three feet deep only served to drain a space of less than five yards on either side, and two ditches of this depth, ten feet apart, left a portion of the Moss between them scarcely affected by the drains.

When the survey of the line was made, only the edges of the Moss could be entered on, and that with difficulty. One gentleman, of considerable weight and rotundity, when endeavouring to obtain a stand for his theodolite or spirit-level, felt himself suddenly sinking, when he immediately threw himself down, and rolled over and over until he reached the firm ground in a sorry mess. Other attempts were subsequently made to enter upon the Moss for the same purpose, but they were abandoned for the same reason, the want of a sufficiently solid stand for the theodolite.

The three resident engineers selected by Mr. Stephenson to superintend the construction of the line, were Mr. Joseph Locke, Mr. Allcard, and Mr. John Dixon. The last was appointed to that portion which included the proposed road across the Moss, and the other two were by no means desirous of exchanging posts with him. On Mr. Dixon's arrival, about the month of July, 1826, Mr. Locke proceeded to show him over the length he was to take charge of, and to instal him in office. When they reached Chat Moss, Mr. Dixon found that the line had already been staked Chap. XI. SURVEY OF CHAT MOSS. 181

out and the levels taken in detail by the aid of planks laid upon the bog. The cutting of the drains along each side of the proposed road had also been commenced; but the soft pulpy stuff had up to this time flowed into the drains and filled them up as fast as they were cut. Proceeding across the Moss, on the first day's inspection, the new resident, when about half-way over, slipped off the plank on which he walked, and sank to his knees in the bog. Struggling only sent him the deeper, and he might have disappeared altogether, but for the workmen, who hastened to his assistance upon planks, and rescued him from his perilous position. Much disheartened, he desired to return, and even for the moment thought of giving up the job; but Mr. Locke assured him that the worst part was now past; so the new resident plucked up heart again, and both floundered on until they reached the further edge of the Moss, wet and plastered with bog sludge. Mr. Dixon's brother residents endeavoured to comfort him by the assurance that he might in future avoid similar perils, by walking upon " pattens," or boards fastened to the soles of his feet, as they had done when taking the levels, and as the workmen did when engaged in making drains in the softest parts of the Moss. Still the resident engineer could not help being puzzled by the problem of how to construct a road for a heavy locomotive, with a train of passengers or goods, upon a bog which he had found to be incapable of supporting his single individual weight!

Mr. Stephenson's idea was, that such a road might be made to float upon the bog, simply by means of a sufficient extension of the bearing surface. As a ship, or a raft, capable of sustaining heavy loads floated in water, so in his opinion, might a light road be floated upon a bog, which was of considerably greater consistency than water. Long before the railway was thought of, Mr. Eoscoe of Liverpool had adopted the remarkable expedient of fitting his plough horses with flat wooden soles or pattens, to enable them to walk upon the Moss land which he had brought into cultivation. These pattens were fitted on by 182 A FLOATING RAILROAD. Chap. XI.

means of a screw apparatus, which met in front of the foot and was easily fastened. The mode by which these pattens served to sustain the horse is capable of easy explanation, and it will be observed that the rationale alike explains the floating of a railway train. The foot of an ordinary farm horse presents a base of about five inches diameter, but if this base be enlarged to seven inches—-the circles being to each other as the squares of the diameters—it will be found that, by this slight enlargement of the base, a circle of nearly double the area has been secured; and consequently the pressure of the foot upon every unit of ground upon which the horse stands has been reduced one half. In fact, this contrivance has an effect tantamount to setting the horse upon eight feet instead of four.

Apply the same reasoning to the ponderous locomotive, and it will be found, that even such a machine may be made to stand upon a bog, by means of a similar extension of the bearing surface. Suppose the engine to be twenty feet long and five feet wide, thus covering a surface of a hundred square feet, and, provided the bearing has been extended by means of cross sleepers supported upon a matting of heath and branches of trees, covered with a few inches of gravel, the pressure of an engine of twenty tons will be only equal to about three pounds per inch over the whole surface on which it stands. Such was George Stephenson's idea in contriving his floating road—something like an elongated raft across the Moss; and we shall see that he steadily kept it in view in carrying the work into execution.

The first thing done was to form a footpath of ling or heather along the proposed road, on which a man might walk across without risk of sinking. A single line of temporary railway was then laid down, formed of ordinary cross-bars about three feet long and an inch square, with holes punched through them at the end and nailed down to temporary sleepers. Along this way ran the waggons in which were conveyed the materials requisite to form the permanent road. The waggons carried about a ton each, Chap. XI. DRAINAGE OF CHAT MOSS. 183

and they were propelled by boys running behind them along the narrow bar of iron. The boys became so expert that they would run the four miles across at the rate of seven or eight miles an hour without missing a step; if they had done so, they would have sunk in many places up to their middle. The slight extension of the bearing surface was thus sufficient to enable the bog to bear this temporary line, and this circumstance was a source of increased confidence and hope to the engineer in proceeding with the formation of the permanent road alongside.

The digging of drains had for some time been proceeding along each side of the intended railway; but they filled up almost as soon as dug, the sides flowing in, and the bottom rising up; and it was only in some of the drier parts of the bog that a depth of three or four feet could be reached. The surface-ground between the drains, containing the intertwined roots of heather and long grass, was left untouched, and upon this was spread branches of trees and hedge-cuttings; in the softest places rude gates or hurdles, some eight or nine feet long by four feet wide, interwoven with heather, were laid in double thicknesses, their ends overlapping each other; and upon this floating bed was spread a thin layer of gravel, on which the sleepers, chairs, and rails were laid in the iisual manner. Such was the mode in which the road was formed upon the Moss.

It was found, however, after the permanent road had been thus laid, that there was a tendency to sinking at some parts where the bog was the softest. In ordinary cases, where a bank subsides, the sleepers are packed up with ballast or gravel; but in this case the ballast was dug away and removed in order to lighten the road, and the sleepers were packed instead with cakes of dry turf or bundles of heath. By these expedients the subsided parts again floated up to the level, and an approach was made towards a satisfactory road. But the most formidable difficulties were encountered at the centre and towards the edges of the Moss; and it required no small degree of in

[merged small][merged small][ocr errors]

genuity and perseverance on the part of the engineer successfully to overcome them.

The Moss, as has been already observed, was highest in the centre, and there presented a sort of hunchback with a rising and falling gradient. At that point it was found necessary to cut deeper drains, in order to consolidate the


Chat Moss. Works in progress.

Moss between them on which the road was to be formed. But, as at other parts of the Moss, the deeper the cutting the more rapid was the flow of fluid bog into the drain, the bottom rising up almost as fast as it was removed. To meet this emergency, a number of empty tar-barrels were brought from Liverpool; and as soon as a few yards of drain were dug, the barrels were laid down end to end, firmly fixed to each other by strong slabs laid over the joints and nailed; they were then covered over with clay, thus forming an underground sewer of wood instead of

« ПредыдущаяПродолжить »