April 2^, 19 16] 



NATURE 



191 



IHE GLACIAL THEORY OF CORAL REEFS. ^ 



SLESS'S demonstration that many of the relative 

 changes of land and sea may be due to variations 

 in the height of the sea, while the land re- 

 mained stationary, and his suggestion that 

 Darwin's theory of coral reefs was as con- 

 sistent with a rise of the sea surface as with a 

 subsidence of the sea floor, were followed by various 

 attempts thus to explain the phenomena of coral 

 islands. This explanation has now received its 

 strongest support in a valuable memoir by Prof. R. A. 

 Dalv, who brings to the problem his usual thorough- 

 ness and ingenuity. His interest in the question was 

 roused by the coral reefs of the Hawaiian Islands, 

 which are so small that they are clearly young, and 

 were probably all formed after the disappearance of the 

 glaciers that once existed around the summit of Mauna 

 Kea. 



After some years of careful study. Prof. Daly con- 

 cludes that the coral reefs of the world consist of a 

 thin veneer of coral limestone resting on a great sub- 

 marine bank; and he holds that the fundamental 

 problem is the origin of these banks, and the recent 

 establishment of the coral reefs upon them. His theory 

 is that coral growth was checked or stopped by the 

 chilling of the tropical seas during Glacial times ; that 

 as the temperature rose the coral polyps started active 

 growth, while the sea surface was being gradually raised 

 by the melting of the polar ice-sheets. Prof. Daly 

 assumes that the ice-sheets of Europe, America, and 

 the Antarctic all reached their maxima at the same 

 time ; and he calculates that the retention of this water 

 on land would lower sea-level by from 27 to 33 fathoms, 

 while the movement of sea water into the polar 

 regions by the lateral attraction of the ice caps 

 lowered the tropical seas another five fathorns. 

 When the sea was thus lowered wave action 

 planed down the great tropical banks and shelves 

 which now support the coral reefs. One of the 

 longest sections of the memoir discusses the depths 

 of coral lagoons, and claims (p. 104) that "neither 

 maximum nor general depths in atoll and barrier-reef 

 lagoons of larger size should so nearly agree if subsi- 

 dence has been the essential control in forming coral 

 reefs." 



The evenness of the lagoon floors may be due to the 

 distribution of sediment by wave action ; for the 

 evidence collected by many authorities, such as Nansen 

 and Stanley Gardiner, has shown that the influence 

 of waves extends far deeper than the limit formerly 

 accepted. The fact that no such great thickness of 

 coral limestone as is assumed by Darwin's theory has 

 ever been conclusively established cannot be lightly 

 -et aside; and Prof. Daly makes the novel suggestion 

 hat the formation of coral reefs may have been 

 stopped by excessive heat as well as by cold. He 

 remarks that when Grinnell Land had a January tem- 

 perature 50° warmer than it has now, the growth of 

 corals in the tropics was probably inhibited owing to 

 ihe lowering of their vitality by excessive heat. 



Prof. Daly has, therefore, adopted the bank theory 



of coral reefs, which, as he remarks, was advocated 



by Tyerman and Bennett in 1832, and in later times 



by Wharton and Agassiz. The part of Sir 



John Murray's theory which explained the depth 



of lagoons by solution is summarily dismissed. 



That Prof. Daly's explanation is correct for 



1 some coral islands may be at once admitted. 



Thus the evidence from the Maldives and Lacca- 



1 dives, which Prof. Daly clearly states, long ago 



Med supporters of the Darwinian theory to regard those 



;^efs as a coral crust upon a submerged ridge parallel 



• "The r,lackl-rontrr.l Theorv of Coral Re^fs." By R. A. Daly. Proc. 

 \mer. Acad Ar's S-i , Vol. li Vo. 4, lO":. pp. 157-251. 



to the Western Ghats. Sir William Wharton origin- 

 ally proposed that one of these islands should be 

 selected for the boring test, but he withdrew this 

 recommendation when it was pointed out to him at 

 the British Association Committee on the subject that 

 these islands would not be regarded as a satisfactory 

 test; so he withdrew his proposal, and at the next 

 meeting recommended Funafuti, which was afterwards 

 selected for the famous boring. Its evidence, however, 

 Prof. Daly rejects on the ground that the bore passed 

 into coral'talus, and that "the actual site of the borings 

 was unwisely chosen " (p. 247) ; but taking all the 

 circumstances into account, the site on Funafuti was 

 probably the best available. 



Glaciation has been summoned to relieve geologists 

 from many difficulties, and in spite of the ingenuity of 

 Prof. Daly's arguments, the Darwinian theory- may 

 still survive this appeal to Glacial influences. The 

 fundamental assumption that all the Glacial ice-sheets 

 reached their greatest size simultaneously seems 

 opposed to the current trend of opinion. The Glacial 

 period was obviously one of widespread earth move- 

 ment; the subsidence of Scandinavia, the British Isles, 

 and northern America during their glaciation would 

 have tended to lower the sea-level; but these move- 

 ments and the amount of water used in the formation 

 of land ice might easily have been masked by uplifts 

 under the tropical oceans. 



One objection to the view that the coral reefs have 

 grown upward to keep pace with a rise of sea-level 

 has generally been regarded as fatal ; for any such 

 movements should have aff^ected the whole of the 

 tropical seas and should have been uniform throughout 

 them. But vast lengths of coast show no sign of any 

 such ris^' of sea-level. In the coral seas themselves 

 some districts have raised reefs, while elsewhere the 

 coasts present the features characteristic of subsidence. 

 This fact was shown by Darwin, and has been con- 

 firmed by the detailed work of Alexander .Agassiz. 

 The grouping of coral reefs according to size and form 

 is also evidence that the coral seas have been affected 

 by differential movements of the sea floor. Dana 

 showed that the coral islands are so grouped as to 

 indicate rapid subsidence along certain lines, while 

 adjacent areas remained stationary. Such facts of dis- 

 tribution apf>ear irreconcilable with the Glacial control 

 theory. J. W. G. 



ILLUSIONS OF THE UPPER AIR.i^ 



A. Review of Progress in Meteorological Theory 

 IN England since 1866. 



The Study of Cyclones and Anticyclones. 



IN 1866, a year after Admiral FitzRoy's death, the 

 Royal Society undertook, by means of the new 

 Meteorological Office, to establish seven other observa- 

 tories in various parts of the country, equipped just 

 like the Kew Observatory at Richmond, and to use 

 the automatic records in explanation of the weather as 

 set out in the daily maps. The explanation of the 

 winds and the interest of the sailor were the justifica- 

 tion of the public expenditure. 



Meteorologists knew about cyclones from Piddington 

 in 1848 and about anticyclones from Galton in 1863 ; 

 from that time onwards until the end of the century 

 the study of cyclones and anticyclones was the 

 dominant idea of dynamical meteorology. 



It was mainly conducted by observations at the 

 earth's surface; and necessarily so. In 1852 Welsh, 

 the superintendent of Kew Observatory, had made 

 four sets of excellent observations of the upper air in 



1 From adisrourse delivered at the Royal Institution on Friday, March lo, 

 by Sir Napier Shaw, F.R.S. 



NO. 2426, VOL. 97] 



