142 PROCEEDINGS OF SECTION C. 



Hedley and Taylor^ strongly support Darwin's theory as satis- 

 factory in accounting for all the features of the Great Barrier Reef 

 of Australia. This had been strongly opposed for this particular 

 reef by Agassiz. 



To return to the more immediate subject of this paper. Very 

 strong and opposite statements have been made in regard to the 

 reefs of the Society Islands, as the following extracts show. It is 

 merely necessary to premise that each of the islands is surrounded 

 by a barrier and a fringing reef separated by a lagoon channel 

 usually J to 2 miles wide. 



Darwin^ : "At the Society Archipelago the shoalness of the 

 lagoon channels round some of the islands, the number of islands 

 formed on the reefs of others, and the broad belt of low land at the 

 foot of the mountains indicate that although there must have been 

 great subsidence to produce the barrier reefs, there has since elapsed 

 a long stationary period." (PI. X., Fig. 1.) 



Endorsed by Dana in " Corals and Coral Islands." 



Agassiz, loc. cit., p. xv. 



"On Tahiti the reefs of the north-west and west coast 

 show admirably how a wide fringing reef may gradually become 

 gouged out into a barrier reef edging a shallow lagoon, and ulti- 

 mately a wide and deep barrier reef lagoon." 



Agassiz, loc. cit. p. 160. 



" In the vicinity of all the ship passes leading into the lagoon 

 either on the east or west shore, numerous islands and islets remain ; 

 outliers indicating the position of ridges or spurs of the volcanic 

 slopes that have been eroded and which once extended to the outer 

 edge of the reef flat." Rautoanui, Iriru, Avopiti Passes are quoted 

 as examples. 



I was naturally keenly on the lookout to observe whether there 

 was any geological evidence of depression or of the influence of 

 marine erosion. The former would evidently be found in the 

 presence of submerged stream valleys and the latter in the presence 

 of steep and lofty cliffs on the shore line of the volcanic rock of the 

 islands, especially at the ends of the mountain spurs. 



Charts of all the Society Islands, except Tahiti, show that a 

 great number of di"owned stream valleys are present, and now 

 appear in the form of deep, far-reaching inlets, such as Papetoai 

 in Moorea, Hamene Bale in Tahaa, and Apumau River in Raiatea, 

 all from two to three miles long. These must be held to prove that 

 the islands are now at a far lower level than when these stream 

 valleys were eroded. 



On the other hand the volcanic rock nowhere reaches the sea 

 level in steep and high cliffs, so that geological evidence of marine 

 erosion appears to me to be entirely wanting. 



Agassiz also lays insistence upon the presence of volcanic out- 

 liers as islands on either side of the ship passes leading into the lagoon 



1 A.A.A.S., Vol. .XI., Adelaide, 1907, p. 413. 



2 "Geol. Obs. on Coral Reefs," ISol, p. 128. 



