Page:Once a Week, Series 1, Volume II Dec 1859 to June 1860.pdf/82

21, 1860.] from the quarries on the hill. Descending again, we turn our steps towards the works, passing on our way a massive breastwork, formed partially of granite and partially of the native stone. We learn that this is an experimental erection, and that in a few days her Majesty’s ship Blenheim, now lying in the bay and bowling great round shot every five minutes along the water at a distant mark, will anchor broadside on, and give the breastwork an impartial peppering, with the view of testing the relative merits as to resisting power, and consequent adaptability for fortifications of the two materials. We believe that batteries will ultimately be built at the extremity of the breakwater, and that the stone of which these are constructed will depend very much on the result of this experiment. A little further on we come to the entrance of the works, and, writing our names in the visitors’ book, are free to wander wheresoever we may choose. Before going further, it will perhaps be well to give a very rapid sketch of the principles and practice of building these sea-walls.

Three methods are commonly in use:—

1st. As at Plymouth. Rubble stone is flung into the water indiscriminately until it forms a bank rising above the high tide level; its sides take any angle they will, and the structure from low water to high water mark is finally levelled and faced with massive ashlar masonry.

2nd. As at Dover. A plain sea wall of great thickness is built (much after the manner of other walls) of large blocks of stone or concrete, laid both under and above water with the care and accuracy of well finished masonry.

3rd. As at Portland. Rubble stone is flung in, until the bank it forms rises to the level of the lowest tides; on this as a foundation a substantial wall of solid masonry is built.

It will be seen that the first method we have mentioned involves an almost incredible consumption of materials; the second takes less material but enormous labour and expense, from the amount of diving and submarine masonry; while the third using less material than the first, and less labour than the second, seems to hit the medium line of the greatest economy possible in these expensive works.

The first object, then, of the engineers here has been to construct this rubble bank; and with this view a temporary staging carried on piles into the water is erected in the following manner. A pile is loaded heavily and sunk into the blue waves, its lower end is shod with a large cast-iron screw, while its top is fitted with a cap, having long radiating arms of wood; the ends of these arms are notched to carry a strong rope coiled round them, one end of which passes to the shore; the arms thus form a kind of large skeleton reel, or drum, wound about with a rope, the loose end of which is then hauled upon by powerful machinery; and the pile steadied by guys, being thus made to revolve, slowly screws its way down into the solid earth, becoming firmer and firmer with each revolution. One row of piles is thus fixed, and another parallel row at thirty feet distance from the first is also screwed into the soil. Upon these, as a foundation, longitudinal timbers are laid, and on the timbers a strong platform erected. We have thus progressed thirty feet into the sea, and the hauling machinery is now worked from the staging thus formed over the spot where the blue water gurgled uninvaded yesterday. Another row of piles at thirty feet distance from the last is now screwed in, and another thirty feet won from the water. Simply told, this is all that is requisite to carry out the wooden staging far into the sea; of the practical difficulties involved in the work we say nothing here; that they are often considerable will be easily inferred, when we remember the great depth of water in which many of these piles are screwed, and the immense weight and size of the piles themselves.

Strictly speaking there are now two separate breakwaters being constructed at Portland, the first running due east from the shore for about 1800 feet; and an outer or main breakwater, which is to be about 6000 feet long, separated from the first by an opening 400 feet in width and sweeping in a circular curve away to the north-east. The first of these, now nearly completed, is not only a sea wall but a landing and coaling stage for large vessels as well, while the outer or main breakwater is at present nothing more than a line of rubble stonework rising above the sea.

Throughout the whole of this length, or nearly 8000 feet, the temporary staging is carried, and its platforms laid with rails for the passage of the trucks of stone. Let us now look a little into the methods employed to procure the rubble and discharge it into the water. On the top of the hill, as already stated, the convicts are at work quarrying the stone. From its summit loaded trucks are constantly descending a series of inclined railways worked by a very familiar arrangement of drums, chains, and breaks, the loaded trucks in their descent hauling the empty carriages up again to the top of the inclines. Arrived at the level of the staging, we see them coupled to a small locomotive engine; and “puff, puff,” away the “Prince of Wales” steams with some six or eight loaded waggons behind.

Leaving the shore, the little engine stands boldly out to sea, supported on the platform and its rails, and rattles by us at a good speed over the creaking and shivering timbers. It is a great sight this, and not without some nervous accompaniments. The deep water is dashing against the piles nearly thirty feet beneath us, yet the “Prince” bowls along over the apparently perilous pathway as merrily as ever Great Western locomotive thundered into Paddington station, its driver and stoker looking as unconcerned as if the waves below them were solid steady earth. Perhaps while still feeling a little doubtful of this new kind of railway travelling the train stops near you, and, without a moment’s warning, without even the sounding of a whistle, you are unmistakeably frightened by a “crash, bang, boom!” as if train, engines, and men had gone together to the bottom. For an instant all sight of them is lost in an ascending column of white water, till as this slowly sinks you again catch sight of the “Prince” quiet amid the din, and then there comes another crash and another column of spray shot high into the air—but this time we are not alarmed; the