GEOLOGY

Nelson Evening Mail, Volume LXI, 11 June 1927, Page 6

GEOLOGY

WEGENER'S HYPOTHESIS

In the course of his remarks on geology itf Bis.,scientific lecture at the ficEW of si?c last evening, »r. I'll; yard, in <jßUw WW Wsgniiers hypotfassi?, or the- hypothesis of CoatinantaJ Drift, said ; Professor Wegqner oases Ins new theory on the principle of isostusy, it sell almost as new as his theory. The central core of the earth is supposed to be quite solid, and has been called the Nife. a word composed of the chemical formulae for the two elements which predominate in it, nickel and iron. This forms a sphere about five-sixths the diameter of the whole world. Above this, nearly another one-sixth is composed of a less dense and slightly viscous mass. the si ma, so named because the dominant elements in it are silicon and magnesium. This is supposed to have been originally covered by a thin crust of still lighter but more solid material, the Sial, named from its most abundant elements silicon and aluminium, and above this was hydrosphere, or universal sea of early times, in which life first appeared. There is a lake in Trinidad formed or black pitch. A piece of this pitch held in the hand feels as solid as ebony, and a. motor-car or even si railway engine can be run out on to the surface of the lake, without sinking. Rut. if yen leave the engine of the motor car standing on the" lake for a. long time', it. begins slowly to sink into it, thus proving that the pilch is really not. a. solid but a viscous liquid. In order to understand Wegener's theory, you must get into your, mind that the Sima is like this pitbh,;.only!, even.7n'pre viscous .still, /so that'movements; in it take great periods of time to accomplish. To complete the picture, you must annex one other metaphor, that of an iceberg floating in sea-water, and recall that for every cubic yard of ice standing up above sealevel, ten cubic yards project downwards below \ that level. Sial and sima being somewhat less similar in densities than' ice and water, this disproportion is not quite so great in their case; but we can. say definitely that there must be a far greater mass of sial below the surface of the sima than there is above it. And wherever the sial rises into large masses, it must be balanced below the sima-level by even larger masses which are thus in equilibrium in their slightly viscous medium. This is the principle of isostasy, that the continental masses are so arranged as to be in static equilibrium in the sima.

EASTWARD SPIN OF THE EARTH

Now we have to take into account another important factor, that of the eastward spin of the earth. If the sima is not solid but slightly viscous, this spin will not only affect the atmosphere and .the hydrosphere, as we already know it does, but, over long periods of geological. time, it must also affect the sial'and the sima. Wegener holds that it was this, spin which originally displaced the sialsphere sot that it began to crack arid' crumple, finally forming a flattish continental block occupying almost half the earth's surface, while the other, half was sea-water. The continental' block thus formed was continually, lagging towards, the westward and underwent periods of great folding and crumpling. Before the block from which our,-continents were carved broke up finally, it. had shrunk to about onetjnrcf.of thei area of the globe, leaving a,vast. Pacific Ocean outside it. Then it. began, to split up by rifting, similar to the great, rift.valleys to be seen in. Africa to-day. One of these formed the nucleus of the Atlantic Ocean and another of the Indian Ocean.- As the pieces.moyed westwards, their forward or western borders tended to crumple np. and. form mountain ranges, while theif. eastern margins dragged behind, flattening out and even 'leaving behind them festoons of island which became particularly liable to volcanic and other disturbance'.. America pulled away westwards' from Europe in the north aU.I from Africa in,the. South, the separation . being completed late enough to allow.qf the. monkeys and other striking frotips of mammals to get a. footing, in puth America.. India pulled away from between. Africa and Australia and cruirip'tecl up northwards to such an extent that the greatest complex of mountain' ranges ever known was formed to the north of it, viz, the Himalayas.! Australia, and. New Zealand were left behind, but slightly pulled away from An-1 tarctica;, to which they had been originally connected. "QREENLAND STILL TRAVELLING EUROPE" Fortunately, this remarkable theory can be actually tested. According to Wegener, Greenland must be still tra-. veiling steadily away from Europe. Old records of longitute taken in Greenland do not agree with later ones, and it appears that a distinct movement has taken place over the last hundred years. But the older records are not as accurate as the new, and therefore it is proposed to make extremely careful observations of longitude in Greenland oyer a long period of years. It mav be that in twenty years ; time a de'finte proof of Wegener ? s hypothesis will thus be found, or possibly it may take fiftv years. Meanwhile, any schoolboy with a. map can take the bulge of Brazil and fit it into the Bight of Benin in Africa, and note how closely it fits, even when all clue allowances are made for coastal erosion. And a geologist, studying the direction and penological composition of tlie ancient mountain ranges on either side of this fit, will find that thev agree completely in all respects. The position at present is that geologists are divided regarding the theory ; this is inevitable for any new idea, which is sure to be resisted by the conservative mind. Biologists, on 'the other hand are nearly all in favour of it» and it may be that this theory.will marl; ;i new turning point in b'iologv and give energy and direction to tlie stud/ of related faunas-and floras. Biologists have long been dissatisfied with the theory of land-bridges to account for close relationships between the animals aii'l plants of widely separated regions, but this new theory makes all plain.' and from the biological point of view it is just what is needed to explain presentday distribution. The test of any theory is "Does it work in practice ?'" Tlie biologist's answer in this case is ''Yes, .i, certainly does, and, moreover it is tne only theory that can possibly work in so difficult a case."