certain point on the coast-line of Massachusetts and New Jersey the inlets and sand-beaches are travelling northward, and at other points southward and westward. But when it is noted that these directions correspond with those of the flood tide along this shore, it indicates more than accidental coincidence."

North of New York harbour the coasts of Massachusetts and New Hampshire are bordered by cliffs of boulder clay and rock

which yield a large supply of sand and boulders. Past Cape Cod the drift of the flood tide is north and then south-westerly into Massachusetts Bay, and the sand has been drifted in the same direction, forming a very remarkable hook-spit, behind which the harbour of Provincetown lies land-locked in complete shelter.

South of New York harbour the coast-line is entirely devoid of cliffs, and the beach consists of sands bordered by dunes, the width being above 3 miles over a length of 80 miles.

From the waters of Chesapeake Bay to those of Biscayne Bay, a distance of about 700 miles, this natural rampart of sand is so continuous, and the lagoons which it shelters so connected, that a small boat could traverse the distance all the way without being exposed to the open sea.1

From the Delaware river the direction of the drift changes from north to south, and barrier beaches of sand extend in an almost unbroken line along the coasts of Virginia and Carolina to Cape Florida. These sand-beaches lie upon the seaward side of large lagoons, the water in some of which is sufficiently deep to provide good harbours.

In the Gulf of Mexico there are several examples of harbours protected by sand-spits. St. Joseph's Bay, which carries a depth of from 24 to 36 feet, and has an entrance through which large vessels can enter, is protected by a long spit; and Mobile Bay is also protected by a similar spit, by which the entrance to the bay has been reduced from 20 miles to about 3 miles, the navigable waterway being only 1 mile wide. The entrance to Galveston Bay is through a narrow opening between two sand-spits. From Galveston to the mouth of the Rio Grande, the coast of Texas is formed by an almost continuous barrier beach of sand, enclosing a lagoon of an area of 1500 square miles. This sandbank is unbroken for a distance of 110 miles.

On the east coast of Africa the tidal current sets along the shore from south to north. Durban harbour is situated in a large inlet or bay having an area of 7 square miles. This bay is completely sheltered by a sand-spit 2 miles long which extends in a northerly direction across the harbour.

These spits are proofs of the permanence of banks of sand in deep water; and if taken in conjunction with similar submarine banks to be found in many parts of the coast in the open sea, show that channels dredged in sand, if properly designed with regard to the set of the tides, will remain permanent without the aid of any training walls. This has been also demonstrated by works recently carried out for the improvement of channels through sand-bars and in sandy estuaries.2

1

A further lesson to be learnt is that a single pier, having a

"The Geological History of Harbours," U.S. Geological Survey, by N. S. Shaler. Washington, 1894.

2 "The use of Suction Dredgers for the Improvement of Tidal Channels," by W. H. Wheeler. Fourth International Navigation Congress, Brussels, 1898.

curved form carried in the direction of the prevailing current, is sufficient for the protection of a harbour. All sand-spits trend in this direction, and there is no instance of two spits running out at right angles to the shore in the way in which many artificial piers for the protection of harbours have been projected.

Sand-dunes.-Low, sandy, exposed shores are frequently bordered by mounds of sand blown off the beach by the winds, known as "dunes" or "denes," in Cornwall as "towans," on the south-west coast as "burrows," and in Lancashire, Cheshire, Lincolnshire, and Norfolk as "meals" or "meols," and on the north-east coast as "bents." Thus the sand-hills at Gibraltar Point,

on the Lincolnshire coast, are described in old maps as "meals." Taylor, in his "Geology of Norfolk," describes the ridges of sand by which the harbours of Cley, Blakeney, Wells, and Brancaster are defended from the sea in north gales as "meals." The sand-banks at Southport are described as "meols," and there are villages in Lancashire and Cheshire having the same name. At Lowestoft they are known as "denes."

These dunes afford protection to the low land lying behind them from high tides, and in some cases advance on the land, covering it with sand, and burying houses and churches, and in some cases whole villages.1

As to the theory relating to the formation of sand-dunes, see paper by Dr. Vaughan Cornish in the Geographical Journal for March, 1897.

But for the protection of dunes on low coasts whole provinces would be covered by the sea, and but for the protection of its dunes there would be little left of Holland and the Netherlands. Kohl says that the people in Holland and Denmark "deal as carefully with their dunes as if dealing with eggs, and talk of their fringe of sand-hills as if it were a border set with pearls. They regard them as their best defence against the sea. These dunes are connected with their system of dykes, and sentries are posted all along their length to repair and guard them against wanton injury."

The sand on dunes is held together by the roots of the grass known as "marram," "star-grass," or "sea-mat" (Psamma arenaria), the roots of which penetrate a long way into the sand. for moisture, attaining sometimes a length of 36 feet, and thus hold the sand together, while the grass checks the action of the wind on the surface.

Taylor, in a paper in the Philosophical Magazine, says that a single plant of mat-grass, which he designates Arundo arenaria, will have lateral shoots radiating from a single stem 10 to 12 yards long, forming a circle 20 yards in diameter, and that a plant of this grass in one year will multiply itself five hundredfold.2

These sandhills retain a considerable amount of moisture, fresh water being often found by sinking wells to a depth of a few yards. Andresen states that the amount of moisture at 1 yard below the surface amounts to 2 per cent. of the bulk, and after rain 4 per cent., and lower down to as much as 33 per cent. by measure.3

Other plants that can live in sand also soon become established, such as the sea buckthorn (Hippophae rhamnoides); the sea wheat-grass (Triticum junceum); sea rocket (Cakile maritima); saltwort (Salsola kali); sea sowthistle (Sonchus maritimus); sand carex (Carex arenaria); sea lyme-grass (Elymus

arenaria).

The mat-grass is sometimes cut for thatching and similar purposes, but this practice is considered detrimental to the maintenance of the dunes. Its leaves are nutritious food for

1 Min. Proc. Inst. C.E., vol. xxi. Paper on Sea-dykes at Schleswig.

2 "Natural Embankments formed against the German Ocean on Norfolk and

Suffolk Coast," Phil. Mag., Series 2, vol. 2, 1827.

3 Marsh, "Man and Nature," quoting Audrescu's " Om Klitformationem."

E

cattle, and it is also used abroad for making cordage and netting.

The protection of these sand-dunes from injury, as already stated in Chapter I., was considered of such importance as to be the subject of legislative enactment.

The growth of the reed or grass can be promoted in bare places, or newly formed dunes, by removing tufts from the older dunes or the inland banks, and planting them in the sand.

On the coast of Holland the dunes are extended and repaired by setting in the sand, in rows about 1 foot apart, tufts of marramgrass. The holes are dug with the hand, the tuft placed in, and the sand pressed round it. One or two rows of reeds are set in the sand, projecting about 4 feet from the surface. The sand drifting along the beach is caught by the reeds, almost burying the tufts of grass, which soon make their way through. As the sand grows up, fresh plantings of grass and reeds are made. By this means bare places in the dunes are extended seaward, and the toe of the slope made good when it has been cut out by storms.

In heavy gales gullies are cut through the dunes, which rapidly increase in width and depth, and through which the water will be apt to run at high tides. These demand careful attention and repair, by making barriers of reeds and bushes, and replanting the marram-grass until the gap is restored. All knolls and vertical faces formed on the seaward face of dunes also should be from time to time levelled and trimmed to a gentle slope.

The bulk of the sand of most dunes is composed of grains of quartz, but in places where shell sand predominates on the beach, the dunes are also composed of this. In Jutland the bulk of the sand consists of yellow quartzite grains mixed with black titanic iron; in gales the dunes are furrowed with alternate ridges and depressions, the former composed of sand and the latter lined with the iron grains. In Prussia dunes are in places sprinkled with oxide of iron, which has given the sand a red colour.

The size of the grains on English dunes varies from 1 to 20 of an inch, the average size being of an inch in diameter. The largest grains are to be found at the base of the dune, and the finest grains at the top.

The slope and surface is greater and more regular on the lee than on the windward face of the latter, standing after a gale at an angle of from 5 to 10 degrees, the slope of the former being about 30 degrees with the horizon.