IN TOUCH WITH NATURE

Otago Daily Times, Issue 22286, 12 June 1934, Page 2

IN TOUCH WITH NATURE

BIRTH OF THE ALPS SAISED FROM FLINTY BEDS, By J. Drummond, F.L.S., F.Z.S, If experts read correctly broken and fragmentary records made in rocks by fossil nlauts, beds on which the Southern Alps were born were laid on the floor of the ocean late in the Triassic Period. This is the lirst period in a great division called Middle Life. The name Triassic, from the trias, three, was chosen on account of a threefold group into which the period is divided in Germany. There it is highly developed, and there it was first studied in detail; but Triassic rocks are found in many parts of the wor-d. The beginning of the period is set down at 190,000,000 years ago, its close at 155.000,000 years ago. These ligures may be little better than a guess. They are supplied by radio-activity, the best system of measurement offered. The scale is acceptable in the absence of anything better. There is also room for error, but this probably is in assigning the Triassic too few milleniums. The world then had entered upon middle age. Triassic streams and livers, lakes, bays, vale,vs, hills and mountains were like the physical features of our own time, but in the vegetation that carpeted the land, cone-bearing trees, horsetails and ferns and their allies predominated, making patterns without much variety, and leaving the landscape montonous and dreary.

Solid, lofty, and stately, the Southern Alps, outwardly, exemplify the everlasting hills. A sketch of their history by Professor 11. Speight shows that they have had vicissitudes. They have experienced the ups and downs of life. They attained a greater height than their European compeers. They were torn and rent by volcanoes, they were covered by icy sheets, and they were brought so low as to be almost level plains. Material for the beds from which they arose, according to Professor Speight, was provided by an old granite-laud, now buried under the Pacific Ocean. Sediments from that granite-land wore deposited on the floor of the ocean, layer upon layer, for millions of years, until they were thousands of feet thick. Tremendous movements of the earth followed. The beds wore compressed and folded. The material arose s:owly until it stood, a towering alpine range, the peaks touching the clouds.

No sooner had the area appeared above the surface of the ocean than processes of denudation began to operate on ft. Levelling continued while the area was being uplifted and while it stood still, and the range was reduced to almost a level plain. The work was so thorough that at the end of the Cretaceous Period ltie last division of the area of Middle Life, all the alpine majesty of the range had vanished. The Alps were represented by only a few masses of very hard rock that successfully resisted destruction. A large part of the alpine range which Had looked down upon hills, valleys and plains was only slightly above sea level. At the end of the Tertiary Era. which geologically was not remote, mouutainbnilding was resumed. The Alps were raised again, this time in the form they still take.

They evidently began in the same way as most of the other great mountain ranges of the world began. To Professor S. J. Shand, of Stellenbosch University, South Africa, an experienced geologist, a surprising thing about present big mountain ranges is that they are formed largely of sedimentary rocks, composed mainly of such stuff as mud, sand, gravel, and shells, and that fossils they contain prove that the sediments were laid down on the floor of the ocean. Most of these big ranges are geological youngsters. They were raised by slow movements, not by sudden hursts of activity. They were not shot straight up. Horizontal movements crumpled the earth’s surface into wrinkles like -wrinkles made in a table cloth when pushed about the table. In a handy little volume, “ Earth-lore, Geology without Jargon,” Professor Shand emphasises this and another strange feature of mountainbuilding. Comparing mountain ranges iu different parts of the world, he finds that the Swiss Alps, the Caucasus, the Apennines; the Himalayas, the Hindu Kush, the Andes, and the Rockies seem to have been raised in the same age of mountains as saw the second rise of the Southern Alps. The periods of uplift were roughly contemporaneous in widely separated places.

Reasons for this are puzzling. Early geologists tried to solve the problem by the theory that the earth’s massive core is cooling, that this makes the crust too big for the core, that the crust accommodates itself to the change of wrinkling, and that the wrinkles force up wide areas into ranges. This is called the contraction theory. Simple and attractive as it is. Professor Shand points out several weaknesses in it. For, one thing, there is the recent discovery that radio-active metals in rocks, notably uranium, radium and thorium, the most radio-active metals known, are continually throwing off heat. This discredits the belief that the earth is becoming cooler. The quantity of radio-active elements in the rocks cannot be estimated. It may be sufficient to cause the earth to become warmer. Professor Shand supports the view that mountainbuilding arises from a deep-seated cause that affects the whole earth at once. He cannot go further than this. He feels that it is best to keep an open mind on the problem, while not losing sight of the contraction theory iu a modified form.

The Southern Alps are not brought into this book. The Napier earthquake is mentioned in order to point out that great earthquakes, although impressive, terrify, ing, and appalling, are less interesting to geologists than slow movements whose importance is noted by only very observant people. During the Napier earthquake the harbour became shallow so quickly that vessels at anchor steamed out to sea to avoid being stranded. An earthquake in the delta of the Indies, 15 years ago, caused 2000 square miles of land to be submerged in a few minutes, and it raised other parts. These upheavals may never be repeated. Slow movements continue for a long time. Great earthquakes are local. Slow changes of level take place almost everywhere. '

In Sweden great earthquakes are unknown, but changes in the relative levels of land and sea there have been measured and studied for two centuries, because of their importance. Fishermen reported that harbours used by their ancestors for generations were becoming too shallow to be used any longer. They saw that reefs and jagged rocks once covered by water were becoming dangerous to shipping. Tide-gauges proved that the northern part of the Baltic coast of Sweden is rising at the rate of two-fifths of an inch a year. In the extreme south of Sweden and on the east coast of Denmark the _ land is slowly sinking. The Scandinavian Peninsula is imperceptibly tilting.

An estimate by Professor Shand is that, at the present rate, a million years would be required to raise Sweden as high as Mount Everest. Less than 10,000 years would be sufficient to spill all the water out of the Baltic Sea and make dry land where water stands at present. The same rate of uplift, continued for the same time, would empty most of the North Sea, and would join the British Isles to the Continent of which once it was a part. Earthquakes are the hare, slow movements are the tortoise.

As lie is a story-teller as well as a geologist, Professor Shawl's book can be read with pleasure by everybody. He has avoided geological jargon that makes many good books unreadable to the general public. Some of them are Greek to the average reader, who craves for knowledge, but lias no time to learn the meaning of many terms in them. Professor Shand writes crisp, clear English. He has taken Joseph Conrad ns a model for his methods. Conrad, be explains, plunges into the middle of an adventure, and leaves a reader to gather pieces of the beginning and hints of the end, and to fit them into the places until n clear picture stands out. It is the only way Professor Shand knows in which to tell the story of the earth. We live in the middle of the story. We can only guess at the beginning. We can hardly conjecture the end.

Coming back to the Southern Alps as an illustration, they wear a crown of glory now. The time may come when they will he laid low once more, when their remnants will slip into the ocean, to lie above the flinty rocks from which their beds were made in the dismal

Triassic days. Thomas Murby and Co., London, the publishers, have attractively produced Professor Shand’s book, which is only 5s net. A novel feature is a window in its jacket. Through the window there ia seen on the cover a coloured diagram of a wedge cut out of the earth from its core to the surface, disclosing i series of rocks in its thickness. '