If a river loaded with send encounter a marine current at its mouth, the effect frequently is to throw up a groat sand-bank or bar, often to the detriment of the nnvigation In the adjoining sea, and sometimes to the entire destruction of a harbour. If such sand-banks be thrown up opposite to the delta of a great river, they accelerate its formation, for the matter brought down, in place of being carried far out to sea, is deposited in the intermediate space, and the sand-bank in time becomes united to the delta.
An extensive waste of the land is in constant progress along every line of coast which presents an abrupt face to the sea. The amount and rapidity of that waste depend upon a variety of circumstances :—the nature of the rocks of which the cliffs are composed, according as they are capable of long resistance, or are easily acted upon by the weather and the sea; the force of the tides and currents ; the greater or less frequency of storms ;—all these accelerate or retard the destructive force of the ocean. In this case also, as well as in the action of running water on the land, the force is greatly augmented when the water is charged with solid matter. The violent surge of a tempest dashing against a cliff detaches large blocks, and sweeps them away ; but the next returning wave hurls them back again against the cliff, and thus a powerful artillery is supplied by the land for its own destruction. When we look upon a map of the world, and see the irregular form and indented line of coast of every continent and island, we have before us the most irresistible proof of the powerful force of the waves, and that the line of the shore must have been formed, in a great degree, by the action of the sea.
The east and south coasts of Great Britain, from the nature of the rocks of which they are composed, and from the violent storms to which they are exposed, are extremely subject to decay. The Shetland and Orkney Islands are laid open to the whole violence of the waves of the Atlantic, and the runs in the Pentland Frith, in ordinary spring-tides, at the rate of 10i miles an hour, and about 13 miles during storms. The steep cliffs on the shores of the Shetland Islands are hollowed out into caves, so that the sca enters in some places to the depth of 250 feet, lofty arches are worn in pro jecting rocks, and almost every promontory ends in a cluster of pillars, obelisks, and towers, the last fragments of extensive continuous strata. In stormy winters, vast blocks are moved from their seat, overturned, dashed into the sea, or carried considerable distances up acclivities. In this case, even rocks of the hardest composition have been unable to withstand the force with which they have been assailed. Islands have been wholly destroyed, and the remains of others rise like the ruins of a Palmyra in the desert of the ocean. Representations of these have been given by Dr. Hibbert in his description of the Shet land Islands, and the following is a copy of one of the most striking.
1792, a portion of land 600 yards from east to west, and a mile and a quarter from north to south, sunk 50 feet in 24 hours. The island of Heligoland, off the entrance of the river Elbe, has been reduced to the fourth part of its size within the last 500 years, and since 1770 has been divided into two parts, the channel between them being navigable by large ships. Nowhere has the sea made greater inroads than on the
coast of Schleswig. The island of Nordstrand, in the earlier part of the 13th century, was separated from the main-land by a narrow stream, and wits 50 miles long and 35 broad, populous and highly cultivated. In the year 1240 a great part of it was destroyed, and at the end of the 16th century it was reduced to an,irea of 20 miles hi circumference. The industrious inhabitants endeavoured .to save their territory by the erection of lofty dikes ; but in October, 1634, a great storm devastated the whole island, destroyed 1340 people, and 50,000 head of cattle ; and three small islets, which have since considerably diminished, were all that remained of the once fertile and populous Nordstrand.
It would be superfluous to give, in this place, farther instances of the like nature : those wo have already mentioned have all occurred within the historical era ; others, however, still more remarkable in 'extent, date from a much earlier period of the earth's history, and the evidence of their occurrence is supplied by the identity in composition of the opposite portions of the separated lands. There is every reason to believe that England once formed a part of France : the cliffs on the opposite sides of the channel are identical with those at the Straits of Dover ; and between Folkestone and Boulogne a submarine chain of hills is, in some places, only 14 feet below the surface at low water. From the German Ocean to the Straits the water becomes gradually more shallow, diminishing, in a distance of 200 leagues, from 120 to 18 fathoms'; and in the same manner, from the Straits to the mouth of the English Channel, there is a gradual increase of the depth of the water, so that at. the Straits there is a ridge with a fall to the west and to the east. In the wearing of the sides, and consequent widening of the Straits, which is now going on, we see only an advanced stage of a work of destruction which has been many thousand years in operation. That Sicily was at one time united to Italy was a tradition in the time of Virgil e 414) :— In the year 1795 a village on the coast of Kincardineshire was swept away by a storm in one night, and the sea penetrated 150 yards inland, where it has maintained its ground ever since. Almost the whole coast of Yorkshire, from the Tees to the Humber, is in a state of constant decay, especially between Flambomugh Head and the Spurn Point, the rate of encroachment at Owthorpe being at present about four yards in a year. An inn at Sheninghain, on the Norfolk coast, built in 1805, 70 yards from the sea, in 1829 was separated only by a small garden from the edge of the cliff. There is now a depth of water sufficient to float a frigate at one point in the harbour of that place, where, only half a century ago, there stood a cliff 50 feet high, with houses upon it. The whole site of ancient Cromer now forms a part of the German Ocean. Dunwich, once a flourishing and populous town, and the most considerable sea-port on the coast of Suffolk, has been gradually swept away, so that there now only remain about twenty houses. The church of Reculver, on the coast of Kent, was nearly a mile inland in the reign of Henry VIll. ; it is now little more than 60 yards from the water's edge.