and are carried out under the direction of engineers specially trained for the work.

The general practice is to give a long seaward slope to the banks, and cover the face with a layer of clay about 3 feet thick, and on this to place a pitching of hard rubble stone-generally basalt from Andernach on the Rhine-in blocks 8 to 11 inches in thickness, or granite boulders from Norway. In some places the basalt blocks are laid on a mattress of osiers, which are either made into fascines 5 inches in diameter and from 40 to 60 feet in length, or packed in layers on the face of the bank. The slope of the lower or pitched part, which reaches to the level of the highest tides, is about 1 in 4, and of the matted part 1 in 40, the length of the face being from 200 to 300 feet.

In other cases the banks for two-thirds of the way down to low-water mark are made to a gentle slope and paved with Dutch bricks; below this the paving is continued with basalt, which is continued at a steeper inclination down to low water. In other cases, instead of the bricks, the clay is protected with a thick covering of plaited straw about a foot thick, placed in layers parallel with the bank, and held in place with straw bands, which are pressed down into the clay with a tool made for the purpose. The straw requires renewing every year at a cost of about 3d. a square yard.

Another method resorted to is the same as that used at Dymchurch, piles being driven into the bank and bays formed with longitudinal and transverse timbers, between which the basalt covering is packed.

Where piles are used in this way, a strong diversity of opinion prevails as to whether the heads should project or be flush with the paving, the engineers in charge of one district contending that these projecting piles serve to break up the waves and diminish their effect; while others--and these are the majoritycontend that any projection of this kind creates eddies which loosen and suck out the stones.

Scheveningen. Here not only the protection of the coast has had to be considered, but also the requirements of an important watering-place, and the long slopes used in other places would have taken up too much valuable space. The sea-defence works are three-quarters of a mile in length, and have been completed about five years. Previous to the construction of the wall the earthen bank was pitched with stones, over which, in heavy storms, the

water broke and fell on the inside, causing considerable damage. This bank, which suffered very severely during the storms of the winter of 1894, has within the last few years been protected by a concrete sea-wall, faced with basalt blocks 12 to 15 inches in depth, the face being formed to a radius of 13 12 feet. The top of the wall is 24 feet above low water, and 13 feet above ordinary and 10 feet above the highest known tides. It is 20 feet high, the base extending 63 feet below low water, and is 8 feet 6 inches wide at the base, and 278 feet at top, the toe being

Apron lin4

Scheveningen.

FIG. 19.

protected by piles driven 13 feet below low water. In front of the wall is an apron 20 feet long, laid at a slope of 1 in 4. The lower part of this consists of mattress-work 13 feet thick and clay; on this is concrete of the same thickness, the top being faced with basalt blocks. The length of the wall is 3714 feet, and the cost was £36 17s. 6d. a yard.

Ostend." The Digue" (Fig. 20), near the Pavilion du Roi, has a solid toe of concrete 16 feet long and 34 feet thick; from about the centre of this is a face of hard burnt bricks. The lower 5 feet is laid horizontally, and above this for 12 feet at a slope of 2 to 1, terminating at the top in a length of 3 feet, having a curve of 3.2 feet, and stone coping; the top being 12 feet 6 inches above ordinary high water, and 7 feet 3 inches above highest tides.

West Kapelle. The island of Walcheren, at the mouth of the Scheldt, is protected from the sea by sand-dunes. On the northwest side, between Domburg and West Kapelle, these were too weak to withstand the sea, and a wall had to be constructed to fill in the gap in the defences, in a somewhat similar manner to that

at Petten; but the exposure here is much greater, the bank facing nearly due north, and being therefore exposed to a fetch of over 2000 miles. The waves beat on this part of the coast with great violence. This bank protects about 70,000 acres of land, the

-Brick Paving

E.H. W.

Concrete

H.W.

OSTEND.

FIG. 20.

surface of which is 6 feet below high water. The tidal rise above low water is 11.20 feet, extraordinary tides rising 586 higher, or 17.06 feet.

The bank dates from the ninth century, but has within recent times been increased in size and consolidated. It is 2.36 miles in length, and its top is 27.38 feet above low water, and 16·18 feet above average high tides.

It was built and is maintained by the Island of Walcheren, the annual cost of maintenance amounting to about £16,000, equal to a rate on the land of about 8s. an acre.

The bank is protected by a series of groynes, the construction of which is described in Chapter VII.

The width of the bank at the top is 40 feet. The average slope is 1 in 14, divided as follows: lower part, for a horizontal distance of 72 feet, 1 in 6, covered with stone up to average high water. All this part is protected by a stockade composed of eleven ranges of piles 6 inches in diameter and from 8 to 11 feet in length, the heads projecting from 3 to 5 feet above the face, and spaced 1 foot 6 inches apart. Above this for 30 feet the slope is 1 in 7, which is pitched with basalt. Above this for 20 feet the slope is 1 in 8; then for 200 feet 1 in 17. This upper part is protected with clay and straw matting. Above this is basalt pitching, and the upper part is sodded. In the less exposed part the face is defended with stone pitching and fascines.

Petten Sea-bank.-For the preservation of the Petten and Hondsbossche Polders on the coast of Holland, about 12 miles south of the Helder, a sea-dyke 3.41 miles in length was built many years ago. This bank was reconstructed during the period 1870-80. The beach in front is entirely sand, and extends from 300 to 350 feet to low water, the slope being about 1 in 60. The bank crosses a gap in the sand-dunes, to which it is joined at each end. The tide here rises about 5 feet, or 2.23 feet above Amsterdam Peil, or mean level of the sea.

During a gale in December, 1863, high water rose 8.20 feet above the level of ordinary high tides, and within 11.48 feet of the top of the bank. During another gale in December, 1883, the waves ran up the bank nearly to the top, or to a height of 18.70 feet above mean high water.

The top of the bank varies from 19.70 to 23 feet above mean high water.

This bank is repaired by two different authorities, the Hondsbossche bank being in charge of the local Polder Commissioners, and the Petten bank under the charge of the Government.

The Government bank is 0.62 mile long, and has a total width of 253 feet at the base, the sea-slope averaging about 1 in 8. The lower part, up to the level of high tides, slopes at the rate of 1 in 4; then there is a stretch of 1 in 40; another of 1 in 24; above this 1 in 20.

The material for the body of the bank was obtained from the inside, at some distance from the work. It is pitched at the bottom up to the level of the highest tides, a length of 60 feet, with basalt from Andernach, on the Rhine, laid on a thick bed of clay. The blocks as obtained from the quarries are hexagonal in shape, and are broken off into lengths of from 12 to 18 inches, and placed on a matting of osiers made into fascines 5 inches in diameter, and from 40 to 50 feet in length. A row of piles, 6 inches in diameter, is driven into the clay about 1 foot apart, the rows being 9.84. feet apart, the heads being left projecting about 3 feet. Above this is a long, flat slope about 87 feet in length, which is thatched with wheat straw laid in bundles overlapping each other, placed on a thick bed of clay, the covering being renewed every autumn. The bundles are fastened down to the clay by bands of straw laid parallel with the dyke, and pressed 6 inches into the clay with a special tool. This straw

covering is only expected to last for one season. The straw thatching is terminated by a row of piles, and above this for about 30 feet is basalt pitching on a bed of clay, the clay covering being continued to the top of the bank.

The Polder, or Hondsbossche dyke, which is 2-79 miles long, has been treated rather differently. The dimensions are approximately the same, the top of the bank being rather higher. Instead of the straw thatching, basalt pitching is placed for a length of 92 feet, at a slope of 1 in 24, up to a level of about 5 feet above the highest known tide; and above this to the top the face is covered with clay to a thickness of about 4 feet.

The cost of the Polder dyke was £183,333, and of the Government bank £41,666, or an average for the two of £63-049 per mile. The cost of maintenance is about £2000 a year.1

The Helder Dyke.-The great dyke at the Helder is described by Marsh 2 as being 5 miles in length and 40 feet wide at the top. It slopes down 200 feet into the sea at an angle of 40 degrees. The base is always washed by the swell of the sea, but the highest waves do not reach the top. The sea-front of the bank is composed of Norwegian granite. Groynes at regular intervals run out from the bank to low water.

On the Friesland coast, over a length of 150 miles, where there are no dunes, the earthen banks have been protected at their foot by triple rows of piles, bound together by longitudinal and cross timbers, the space between the piles being filled in with stones. The ground adjacent to the piling is secured by fascines, and at the more exposed parts heavy blocks of stone are heaped up as an additional protection.

Cranz is a sea-bathing resort on the shore of the Baltic standing on a cliff consisting of loamy clay from 16 to 20 feet high. This cliff was gradually being undermined and washed away by the action of the sea. About 40 years ago some short groynes were constructed in front of the cliff, but, not being carried high enough up the beach, did more harm than good; the waves breaking above them cutting out the beach, a current was set up between the upper ends of the groynes and the cliff, which caused considerable erosion. Subsequently these groynes were carried up to the foot of the cliff, and extended seaward to a depth of 5 feet.

1 Centralblatt der Bauverwaltung, January, 1898.

2 66 Man and Nature," Marsh. 1864.