ORIGIN OF SAND.

Kaipara and Waitemata Echo, 28 October 1920, Page 4

ORIGIN OF SAND.

ENCROACHMENT PROBLEM. The sand problem cm the Kf.ipara coasts has not had much prominence lately, but we undeistand the committee recently formed in connection with the matter of checking the gradual drift wnich is all ttie time taking place is still alive, and keeping in touch with any move likely to' be made by the Government in this respect. Tho distribution of sand on the coast depends, in the first place, on marine waves upon the rocks, but it is generally admitted that this is not sufficient to account for the vast quantity of sand that borders ourbeaches. Undoubtedly a very conitderable portion represents the mate* rial carried to and toward the ocean, by the storms and glaciers of the Ice Age. It is calculated that nine-tenths of the coasts of the ?*orld are covered with sand. What is the origin of :his sand and to what circumstances s its abundance due ? Men of science tmve explained this in part by saying that it is due to the erosive effect af the currents and the topographical ispects of the coasts themselves. Where there is no protection in the shape of cliffs the coasts aie covered with enormous quantities of sand, but its advance is checked by plants and vegetable growths. Sprouts, trailing vines, or dragging roots serve the purpose of keeping the sand in place and giving consistency to the appearance of the average beach. Of these vegetable growths, those are cal~ dilated to serve the purpose best which are most abundant and whose resisting power is strongest. In the time of Elizabeth a law was passed prohibiting the destruction of such beach plants as they tended to keep back the sand otherwise carried by wind and lain to the detriment of crops. It was thus early recognised that plant life had an influence not to be dispised m the formation of sandhills such as one sees iv such plenty on the coasts of England and Flanders. These banks, called ''dunes," are either stationaiy or moving, as the case ma)1 be. When the sand deposited on the coast by the waves is not excessive and the wind blows in termittontly, ono may see behind the handhill the vegetable growth that is giving solidity to the mass from its roots up. In this waj are formed the stationary dunes. When the vegetation is extended as far as the sea the dune grows in this direction and the curious spectacle is presented of the ocean receding before the advance of the coast. A well-known building in Southport, EnglaLd, was built on a beach formed in just this ">vay. The moving dunes, although the same in origin as the stationary ones, owe their special characteristic to their great mass nnd the direction and constancy of the wind, which prevents their finding a base strong enough to constitute a hold on the eaith. These dimes are tossed about, oftoa advancing into the interior over cultivated ground to the despair of farmers. On the coasts of Gascony there are points where the dunes push forward more than four yards annually. In 1780 the advance of sand upon the land of Bordeaux was the occasion of despair of horticulturists and crop growers, and the engineer Bren.ontier made himself famous by convert-* ing movable dunes into stationary ones. The task was undertaken to form a wull against thp sand invasion by making a palisade of the dunes a little more than a metro high, and pnting planks between each pair. When the sand swept over the board it had to break up its volume in the effort, and little by liitle a stationary dune would form with an inclination of from(eeven to twelve degrees in the direction of the sea. Behind this palisade was conveniently disposed a wider zone of the hardier shrubs. Fiance is by no means the only country that has undertaken to con test the advance of the sand. In Holland and also in Denmark the problem has been studied for centuries.