EARTH'S EVOLUTION.

New Zealand Herald, Volume LXV, Issue 20074, 11 October 1928, Page 8

EARTH'S EVOLUTION.

ENDLESS EROSION. THE SWISS LANDSLIDE. FATE OF ALL' MOUNTAINS. WASTE AND RECONSTRUCTION. "A countryside faced with the greatest avalanche Europe has ever known." With these words the Monte Arbino landslide, which occurred last week, was recently predicted in a London newspaper. The statement, of course, is as incorrect as the terms "eternal lulls," "enduring hills" and the "changeless decree" of the hymn. Humanity is prone to mea, sure time by human history and to regard the physical features of the earth as permanent. But

The hills are shadows, and they flow From form to form, and nothing stands; They melt like mists, the solid lands, Like clouds they shape themselves and go. Tho finger of fate is on the mightiest of mountain-chains, said Greenly, who in a brief work- has endeavoured, with considerable success, to bring the outlines of geology within the comprehending vision of the ordinary man. Tho very same powers which have carved the mountains into majesty are destroying them, night and day, without remission, and, geologically speaking, a time is not far distant when every vestige of those white peaks will be sleeping upon the bottom of the ocean. Again and again has this taken nlace; tracts which are now quite low have alpine structures and they aru the worn-down roots of vanished mountains of old time. The combined effect of the destructive agents is to reduce every country to a plain at sea-level. In fact, but for the counteractive effects of the movements of the Lithosphere (tho shell of the earth) all land in the world, at the pre sent rate of waste, would be swept down into thij sea in some five or six million years, and that is but ;i fraction of geo logic time. A land surface, accordingly, is but a passing and fleeting phase ol change. Minor Slips in Process. The collapse of the summit of Monte Arbino, which has destroyed three peaks and filled valleys 4000 ft. below, is just one step in an unceasing process. The contour of the mountain has been changed for more than one mile and the news has been flashed round the earth as the "greatest avalanche Europe has ever known." Actually, it is just one minor movement in the inevitable evolution of the earth.

Destructive agencies are never still. Just as frost causes the bursting of water-pipes in cold regions, so mountains are steadily being worn away. Water that finds its way into cracks in the rocks expands on freezing and forces the sides of the cracks asunder, so that when thaw comes the loosened fragments fall away. At the feet of crags we often see long trains oi "scree" composed of angular blocks de tached in this manner. In the tropics a similar effect is produced by the great difference in temperature between day and night, giving rise to rapidly alternat ing expansion and contraction. But rocks disintegrate in another way Just as iron rusts away when exposed to the weather, so do rocks. The crust becomes soft and the products of decom position being soluble in water are car ried away invisibly. This is called "weathering" and, incidentally, the pro cess is vital to animal life, because it is the decomposition of rocks that provides soil, without which there would be no vegetable life and hence no food. Px-ob-ably the Monte Arbino landslide is the result of the "weathering" of thousands of years which, by slow degrees, wrought changes that exceeded the angle of repose. Water and Glaciers. Deluges are often rapid destructive agents. A sudden downpour on a Welsh mountain in 1900 cut a channel 20ft. deep and moved blocks of 280 cubic feet. Vast quantities of rock, and "earth" aie washed away in such spates, the fragments. being ground away as they are pushed down the rivers and the products of erosion in the end find the sea floor. Glacial's also are destructive agents. Tlio vast rivers of ice carved deep valleys and ravines in mountain sides and helped to put the mark of fate upon the. peaks. Sea, coast erosion is constant. Storm waves batter the cliffs, sometimes using loose blocks of rock as projectiles which cut and break and crush their feet awl prepare for slips and landslides. Five hundred years ago, King Henry IV. landed at the port of Ravenspur in Yorkshire. The site of Ravenspur is now a mile from the coast. Such has been the coastal erosion in a few centuries. Every land-surface is a scene of unremitting waste. Most, of it is done so unobtrusively that it is rarely noticed. Theatre of Construction. The waste goes on and on. What then? Just as the land is the theatre of destruction so is the sea the theatre of construction, for the vast deposits on the sea-bed create the conditions whereby, through subsidence of the water or elevation of the bed, new land masses are mads for another cycle of erosion Through pressure on the silt of ocean floors sedeincntary rocks are made, and such rocks compose most of the land today. Almost the whole of England is of this nature, and those, who have dug fossilised sharks' teeth from limestone rocks at high levels in New Zealand do pot require to have studied the subject to know their origin. Silt and mud is the visible sediment from erosion. The invisible products of waste have their share in the const ruc•e process, for they are taken up hy various marine animals which build shelis or frame-works of calcium carbonate or silica. Thus does the "weathering" of mountain heights lend to the. deposit of vast, quantities of shells on ocean beds and to the building up of coral reefs, which are another feature in the reconstruction of the earth. Volcanic Action. Other constructive agencies are volcanoes, the work of which in New Zealand is self-evident. Construction by volcanic action is sometimes rapid. In 1538 Monte Nuovo, on the shore of the Bay of Baiae, rose to a height of 489 ft. in 48 hours. Submarine volcanoes pour ere at quantities of tuffs on to the sea-bed. In 1831 a cone rose 600 ft. and cmerrred as a small island known as Graham's Tsland, but it was washed to sea level in a few months. There has been similar action recently in the Pacific. The terrific convulsions which upraise the strata of ocean beds and fold and twist them, and by overlapping raise lofty peaks, would certainly draw the most sweeping superlatives from the journalistic observer, but the last of these if) not to be found in the files, and we may have to wait a few million vears before a new continent rises. Doubtless the League of Nations will have an anxious time subdividing it. But "tho dust of continents to be" is constantly pouring down the rivers of the world, and in the rock into which it will be compressed, scientific beings of the future will search for the sort of skulls wa are now wearing.