Nature has provided, in the mighty bank known as the Chesil Beach, practically a great shingle embankment, protection to Portland Harbour on the west and south-west, and the object of the breakwater was to secure, by engineering art, a similar protection to the bay on the south-east side. The Chesil Bank, though now and for long perfectly impregnable to the tremendous rollers of the south-westerly gales, was not always so, and as late as the reign of Henry VIII, great breaches had been temporarily effected by the power of the sea. Still it affords a splendid protection, as does now the mighty double breakwater designed by Rendel, and brought to completion by Coode. The breakwater leaves the shore at the north-eastern extremity of the island, and runs out due east to a distance of 600 yards. “This inner limb alone,” wrote an authority in engineering,[65] “is a splendid achievement of human labour and skill. It has been top-finished by a grand superstructure of hewn granite, and ends in a circular head, which has been completed as a fort and mounts eight guns. The foundations of this massive bastion have been most carefully planned, with especial reference to the safe passage of the largest vessels through the 400 feet gap which the fort flanks on one side. The masonry is continued in a perpendicular line to a point 25 feet [pg 194]below the lowest water-line of spring-tides. A ship of the line, as is well-known, draws at the utmost 24 feet. An extra foot of perpendicular masonry, therefore, having been allowed, the lower masses of the fort begin to slant outwards, and continue to do so till they reach the firm clay bottom. This lower portion consists of a well-consolidated mass of unhewn stone. The outer, and by far the longer limb, of the breakwater begins to bend away to a point very near due north shortly after leaving the gap, the further side of which is also flanked by a circular head.... The whole of this vast outer limb, with the exception of the circular head at its inner extremity and a fort at the other end, consists of nothing more than a stupendous bank of rough unhewn stones of all shapes and sizes, tumbled out of the wagons on the timber staging above. Divers, constantly employed, have effectually prevented the chance of any holes being left in the rising mass, and have been able to indicate the precise spot over which a given number of loads were required to be ‘tipped.’ The security of the bank is further guaranteed by its enormous width at the base; and although the waves have already rounded many a giant block below the water-line and made it look as if its present place had been its abode ever since the Creation, yet this polishing and grinding is the extent of the effect which they will be able to produce upon a work probably destined to hold its own as long as Portland itself.”
The rapidity with which the breakwater was constructed reflected great credit on Mr. Coode. The actual routine of the construction followed, when the line for the structure had been sounded and carefully marked out, was to commence piling for the railway that was to carry the long trains of wagons filled with the stone; and when a short piece of this was completed, to go on “tipping in” the rubble and rough stone till they made their appearance above water at last; then the piling was carried forward a few yards more, and the process repeated, and so on by successive stages to the completion of the work. All appears very simple on paper until we learn that it had to be accomplished through eleven fathoms of rough tumbling waves. One night’s rough weather often swept away the timber-work that cost many thousands of pounds, and many months of labour to construct and fix in its position in the sea. The piling that had to resist the action of a deep and heavy sea, and to carry also, at a height of 90 feet, a railway for the heaviest traffic, required to be something more than a common framework of timber. Every log used had to be first of all saturated to its very centre with creosote, and this was done in a most ingenious manner. A great boiler, 100 feet long and 7 feet in diameter, was filled with the largest and finest logs procurable; the mouth being closed with a solid air-tight cover, the air was pumped out, not only from the tube, but from the very pores of the wood itself. When the vacuum was as complete as possible, the creosote was admitted from tanks at the bottom and forced into the timber by hydraulic power of about 300 lbs. to the square inch. In this the logs remained for two or three days, by which time the creosote was forced into the fibre of the wood. Several of the logs thus prepared were bolted and bound together, till one huge spar 90 feet long, and eight or nine tons in weight, was formed. Then an iron “Mitchell” screw—as used in the lighthouses built on sands, already described—was affixed at the lower end, and the whole sunk till it rested on the bottom, when it was worked round by a capstan till it was firmly screwed into the clay. Thus secured, they were tolerably safe, though single heavy waves would uproot piles and moorings together, to obviate which [pg 195]two or three piles were generally set at the same time, and well bound together by powerful cross timbers.
The stone quarried for the breakwater from the very top of Portland Island was largely excavated and brought to the spot by convict labour. The stone itself used was unfit for architectural purposes, but quite suitable for the breakwater. The convict prison, also on the top of the island, was virtually the barracks for 900 labourers, who were more profitably employed than in walking a treadmill or picking oakum. The quarries were some 400 or 500 feet above the level of the breakwater, and the stone was conveyed to it by three inclines of broad double gauge rails. The trains of trucks or wagons were worked up and down with a wire rope over a drum, the weight of the loaded descending wagons winding the empty ones up again to the quarries. A powerful locomotive pushed the loaded trains to the end of the work, where the stone was tipped into the sea, as much as 3,000 tons a day having been sunk at Portland. The total amount so committed to the deep was about 5,360,000 tons, and the area protected by the breakwater would accommodate sixty of the very largest men-of-war, and almost any number of smaller vessels.
“During the progress of the works,” wrote Mr. Moule, “the engineer has from time to time instituted some highly interesting investigations into the structure of the Chesil Bank.... During a single night’s gale, between three and four millions of tons weight of pebbles have been found to be swept away into the gulfs of the Atlantic, being gradually thrown back again in the three or four following days. The size of the pebbles had long been observed to vary greatly at the two opposite ends of the beach. At the western, or Abbotsbury end, they are exceedingly small, more resembling gravel than shingle. At the Portland end it is not uncommon to meet with them several inches in diameter, and several pounds in weight. This phenomenon has been explained by the very probable assumption that the pebbles are driven eastward by the wind-waves, and not moved by the slow and (for purposes like this) powerless tidal current. The larger pebbles, presenting a broad surface to the waves, are easily rolled forward, while the smaller ones are passed by, offering a less surface, and becoming more easily imbedded in the sand.” It is said that a practised smuggler on that coast could tell his whereabouts on the bank in the darkest night or thickest fog, by feeling the size of the pebbles on which he stood. And smugglers and “wreckers” were once very numerous among the Portlanders. In these better days their courage and great personal strength has saved many a life and ship endangered off the bank.
An old and popular song says that—
“Britannia needs no bulwarks,
No towers along the steep,”
but recent legislators have evidently not been so thoroughly satisfied of the fact, or they would not have authorised the construction of the great fortifications at Portland, which make it almost the Gibraltar of the Channel. The splendid breakwater there did not need protection. All the battering it is ever likely to get could not injure it seriously, and whatever ruins Macaulay’s New Zealander may stand upon, they are not likely to be those of a great breakwater, each year of the existence of which renders it generally more compact. But it was for good reasons that the extensive works of Portland were undertaken. “We,” said the Times, “of [pg 196]all people in the world, who so toiled and suffered, lavishing blood and treasure under the walls of Sebastopol, should be the last to underrate the importance of a good fortification as a check to an invading army.” The reader will hardly require any defence of such policy, for naval arsenals contain the very germ of our power, as the iron safe of the prudent man contains his valuables.
The Bill of Portland greatly resembles the situation of Gibraltar. There are the same bold, steep, rocky headlands; the breakwater stands in place of the Mole, and Chesil Bank connects it with the mainland, as the neutral ground does our great Mediterranean citadel with Spanish soil. “Its height, its isolation, and the harbour it commands, all pointed it out as a place for an impregnable—we had almost said an inaccessible—fortress. To the late Prince Consort is due the credit of having seen its vast importance in this respect, as it was also owing to his enlightened judgment that the breakwater was begun at last, and he himself laid the foundation-stone. Portland is rising, as we have said, into a first-class fortress, of which the Verne is the great key or citadel.” So spoke the Times, in 1863; and now Portland is the best fortified port and naval station in the kingdom.
The Verne is a height which, like La Roche at Cherbourg, dominates over all around it for miles, especially on the side which overlooks the breakwater and the sea. On the north side it is protected by nearly perpendicular cliffs; elsewhere it is fully protected by art. One of its greatest defences is the dry ditch which completely encircles the whole work, except on the north side just mentioned, where it is both unnecessary and impossible. This ditch is one of the greatest ever undertaken in ancient or modern days. Its depth is 80 feet, and its width 100, and in some places 200 feet; its length is nearly a mile, and its floor is 368 feet up the hill-side. Nearly two million tons of stone had to be blasted to form it; and it would never have been excavated on the colossal scale indicated, but that all the said stone was utilised in building the breakwater. With this tremendous artificial ravine to [pg 197]cross, with fortifications and bastions fully prepared with heavy Armstrong ordnance towering above, what enemy is ever likely to attack the citadel of the Verne? Our leading journal spoke of it as more compact than Cherbourg, Cronstadt, or Sebastopol, while it is more than three times their elevation above the sea.