CORAL REEFS

Dominion, Volume 7, Issue 2168, 5 June 1914, Page 8

CORAL REEFS

AND HOW THEY ARE FORMED PROFESSOR DAVIS SUPPORTS IT* 'At Victoria!. College last night, under tho auspices of tho Wellington Philosophical Society, Professor W. M. Davis, of Harvard University, delivered a lecture on tho origin of tho coral reefs of I'm. . Professor Davis is nn honorary m 9^°P? ..«f the Now. Zealand Institute, '\ ncl J.l'.y's.'ting tho Dominion as ono of the invited American guests, in ■conjunction with the.visit.of tho British Association for tho , Advancement of bcKsnce. Ho has recently made a special study of the coral reefs of Fiji, and his "address last night, was full of interest, .There was an.attendance of about-twohundred people; Dr..Hector, president of the Philoso-' pluaal.. Society, presided, and in intro- 1 uuomg Professor,Davis, said that it was a rare pleasure to have an honorary, member of the Now Zealand InBtitute lecturing to them. Professor Davis was, he said, a master of lucid explanation.. , . Professor Davis, sought tho aid of diagrams to show three formationsfringing reefs, barrier reefs, and atolls —which confronted the investigator m research work connected with coral formation. . 'Fringing reel's, .wore islands with a fringing border of coral, barrier, reefs were islands surrounded by a coral barrier. Many theories, ho said, had heon advanced to'account for tho different formations, but all authorities agreed that the coral insects lived only in wator less than 25 fathoms in depth.

Three Important Theories. The threo most important theories to account for fringing reefs, barrier islands, and atolls were those put forward by tho eminent oceanographer Murray, by Agassiz, and by Darwin. Murray's ; theory was that a still island, formed by volcanic eruption, became -fringed with coral growth in tho shallow water. The reef, ouce established, grew out on ■ its own formation, and terraces wero , established by the coral breaking away. In that way a wide terrace was evontually formed. While it was, in process ' of formation (according to tho theory), the inner part of the reef died, and was ■ supposed: to dissolve. As tho island was also wdni away;-a lagoon formed, and the atoll was established. Passing to tho theory of Agassiz, the lecturer showed by illustration that an island was first/supposed to exist.' 'Tho action of .the, sea cut into.tho,sides of.tho island, and made ■ a broad platform on which coral growth could start. In Darwin's theory' a■-newly-made volcanic island Was supposed, on which a fringing' reef Iwas introduced. In tho course of timp the volcanic island was supposed to sink,'while.the fringing coral gradually .'.'grow, .up towards tho surface j of thojsea. ~,.,The-.island.continued:"to' 6ink.-p.iuT the coral, reef continued to grow, so that eventually a lagoon was formed. ■'..'.■.. All Were Conceivable. > ' All"'three theories, "said the-Profes-sor, were conceivable,'but tho question was: Did ,such action tako„placq? ..It seemed that they could not solvo tho problem as to whether.the theorios wero possible by looking: at'.tho reefs themselves. It-had been suggested that boring in the. centre of an atoll would estab-lish-conclusive proof, and boring had 'been resorted to in one; atoll, with tho result that a thousand-febt'of coral rock' was""disclosed. It .was. a difficult and expensive; task to-bore! all'«toll, : and, unfortunately, the results were uot conclusive. Fringing reefs did not need any ■ discussion, bub-atolls stood alone, and had no story to tell as to how they had been formed. Barrier reefs were significant, for therd ' was ' a central, •island, and .something.must.'have been' going on thero.' To tho. investigator' was left the task-of studybg tho nature •of proof) or finding -how- ho-was right.

y'> Two Theories -Discounted. Taking-each theory'separately.,' Pro-' fossqr.Davis showed what wo'ild havo been left in, each ease. If MurTay!s,.theory.of..a still-standing. island were, correct, deltas should,have: been formed by its dissolution; ail irregular coral'.rock: bottom found-.to the lagoon, .or s"dmo r insoluble Tesiduo left by the . dissolving island, and, as there were a good many atolls, in tho Fiji - Islands, some."almost atolls" should havo cx- , istod, Mowing' ovidence, 'of the. volcanic -island: After investigation had' been r mado, it had been found that tho consequences wero absent, so that Murray's ■theory did not produce "the associated' features. The theory of Agassiz, also, could not stand, for, had tho sea washed away tho island to form a platform, that platform would havo been bordered by rising cliffs', and that was not the case.-' . One Stood the Test. Darwin's theory seemed to stand tho test, especially in one feature. It. was safe to say that if a simple 'island (an island with an oven foreshore). sank,one of the consequences, accompanying slow subsidence .would bo tho formation ofmany bays'round the island. All tho reefs charted poscssed thoso indented .foreshores, thus giving direct evidence 'in favour of Darwin,'.? Itheory. 'D,a'nvin was apparently satisfied with his theory, and did uot inquire any further. That was unfortunate, as it was not •sufficient to accept a theory without inquiry. Independent-confirmation -had, however, been given. .In conclusion, '.Professor Davis said that during his visit to Fiji in March and April ho visited eighteen islands, and all had f-howit indented foreshores. Ho hoped to visit New Caledonia, Now. Hebrides, and tho Society Islands. In thanking Professor Davis for his lecture, Dr. Hector said that he was glad to find that Darwin's theory had been supported by tho lecturer.