CRUMPLED FOLD.

Waikato Times, Volume 109, Issue 18255, 17 February 1931, Page 11

CRUMPLED FOLD.

LAND FORCED UP. A GEOLOGIST’S VIEWS. In a statement given to the Sydney i Morning Herald 'Professor Sir Edgej worth David, the eminent geologist, I said that In regard to the earthquake shocks at Napier, most of the severe shocks in various parts of the world were due to a progressive wrinkling of the earth’s crust as the earth became older. He said the tendency was with the j advancing age of the earth for the| ocean basins to become deeper and for | areas of land around to be crumpled up into folds or wrinkles. In the land areas, the material of its rocks was lighter in weight than the rock material which formed the floors of the deep oceans. There was a tendency with time for this heavy material In the ocean floors to sink deeper towards the earth’s centre, and in so doing the lighter material of the lands around the oceans was forced upwards. Thus, if one took a stretch across the Pacific from New Zealand to Chile it might he compared to a bridge the crown of I which was so heavy that the abutments were unable to sustain the weight so that the centre of the bridge slowly subsided, and in so doing caused a heavy thrust against the. .abutments,

which may be bent or crushed in the process. In the ca’se of New Zealand, the North Island had been compared to a boot upside down with the toe in the direction of Auckland pointing towards Norfolk Island, New Caledonia, and then to New Guinea. The heel pointed in the direction of the Kermadeo Island's, the Tonga or Friendly Islands, and then on to Samoa. Especially Notable. What was especially notable in the case of the recent earthquake was that whereas there were a number of earth folds traversing the triangular area, there was only one important fold j along the line just described to take up the stupendous thrust which came | up against It a's a result of the downward movement of the ocean floor. This great fold was continued to great depths in the sea, as, for example, the Tonga Deep, which is part of the deep ocean which extends all the way from the east of New Zealand to near Samoa. 'So profound is the depth that if Mount Everest, whioh is some 29,000 feet high, were cast into the deepest part it would be completely submerged. Sir Edgeworth said that it might be some satisfaction to know that, there was a part of New Zealand where the great fold or rock rampart was strongly buttres'sed. That was the part of the South Island south of Timaru, through Dunedin to Invercargill, and right across Lake Wakatipu to Milford Sound. There the great earth fold bends round so a's to 1 meet the thrust from the Pacific edgeways on, and it formed an extremely strong and resist-

ant structure to 6arthqu&&® s - Front the Bay of Plenty In the direction or Auckland and North Cape, the rook structures also formed a buttress, though not quite so strong as at Dunedin. Relieving Pressure. It was devoutedly to be hoped that the result of the shocks of 1929, and the present earthquake would have the effect of relieving these vast earth pressures for some considerable time to come. At the same time, it was premature to predict what might happen until further data was available. These earthquake shocks were Australia's first line of defence against the tremendous pressures coming from the Pacific Ocean. I ‘‘But for this mighty bulwark,” said Sir Edgeworth, “the thrusts' from the Pacific would make themselves felt along our shores, and Sydney might share the same fate as Napier.”