THE GEOLOGY OF FUNAFUTI. 85 



at least 8 feet to account for the fact that this disintegrated material became firmly- 

 cemented in situ by Lithothamnion. But this alga cannot live for more than about 

 1 foot to 2 feet above the level of low tide, and even in these cases it is necessary for 

 it to be continually bathed by the spray, if it is to remain alive. 



As much of this Lithothamnion-ceraented breccia is now fully 2 feet above high 

 water, and, as the tides at Funafuti have a range of about 6^ feet, a rise of 

 the sea of 65 feet would be necessary in order to bring the present top of this 

 breccia sheet down to the zone of living Litliothamnion, the upper limit of which is 

 about 2 feet above low- water spring tides, as just stated. At the south-west end of 

 the islet of Telele an outlier of this breccia rises 10 feet above high water. Since 

 this has corals in situ in it up to that level, and is cemented in the usual way, 

 a rise of the shore-line of even as much as 14 to 16 feet would be necessary in order 

 to submerge the summit at low tide, and so admit of the growth of the corals. 



There is no definite evidence that any islets were formed during the growth of the 

 old Heliopora cmrulea and Porites reefs, but during the subsequent slight downward 

 movement, followed by erosion of the preceding reefs between tide marks, the 

 material thus eroded was probably piled up so as to form long islands. Subsequently 

 these were submerged, and their materials spread out by waves and currents, and 

 consolidated by Lithothamnion, &c., so as to form the breccia sheet. 



This submergence amounted to probably about the extent of the maximum 

 thickness of the breccia sheet, or at least 5 to 6 feet. A re-emergence of the 

 atoll followed, the reef platform now consisting of Heliopora and Porites reef below 

 and a breccia sheet above. By this re-emergence a continuous strip of land was 

 formed from the Bua-Bua Passage to Pava, and probably from the north end of 

 Mateika to Te Ava Fuagea. Isolated masses of breccia were also developed at 

 Fuafatu, and probably on other portions of the atoll rim between Te Ava Fuagea 

 and Pava. The hard breccia sheet, brought now within effective range of the 

 battery of the heavy surf, became completely cut through in places, the portions 

 which best resisted denudation forming the hard substratum of the present islets. 

 Meanwhile, masses of breccia would be dislodged from the ocean platform on the 

 eastern side of the atoll, and from the lagoon j)latform on the west side, by the 

 waves raised by the trade-winds, while, during the seasons of the north-west 

 monsoons, the breccia would be attacked on the ocean platform of the west side of 

 the atoll, and on the lagoon platform of the east side. By this means a double line 

 of Hurricane Banks was thrown up both on the east and west sides of the atoll, 

 so that, on both these sides, were raised an inner and an outer bank, which, classed 

 on the basis of the agent which formed them, might be indicated in order thus, from 

 west to east : — 



Outer N.W. Monsoon Bank. 



Inner S.E. Trade Bank. 



Inner N.W. Monsoon Bank. 



Outer S.E. Trade Bank. 



