Inlands and Coral Reefs of Fiji. 419 



gigantic pothole, from vvhicli tlie cliurned material is carried out by 

 the currents flowing through the entrances into the lagoon. It has 

 long been known that there is a violent rush of water out of the 

 lagoons, the velocity attained reaching sometimes four to five knots. 

 In Fiji I have noticed these powerful currents flowing out of the 

 passages leading into the lagoons of Fulanga, of Ngele Levu, of 

 Wailangilala, of Vatu Leile, of Totoya, and racing along the interior 

 channels of the great barrier reef stretching along the south coast 

 of Viti Levu, especially at Lauthala Bay, Suva, and the reef harbors 

 and passages between Suva and Serua, and out of the smaller atolls 

 like Motua lai lai, Thakau Leka leka, Thakau Momo, and others. 



" The strength of the currents in the channel separating the 

 barrier reef and the shore has been noticed by Semper and by 

 Mobius as bearing an important part in Mauritius. There is in the 

 Biologisclies Centralblatt, 1889-90, Bd. ix, p. 564, a short review 

 of the third edition of Darwin's ' Coral Reefs,' showing the principal 

 points in the discussion of the reefs to wliich Bonney has called 

 attention. But this discussion is mainly theoretical, and adds no 

 new factors in the problem. I would refer to what Gardiner says 

 regarding the conditions affecting the growth of coral reefs in Fiji, 

 where he shows the effect of tidal currents in the passages of reefs 

 and inside of reefs. Strong currents prevent tlie coral larv^ from 

 fixing themselves in localities which they scour, while the corals 

 will thrive off the passages where the currents have lost their 

 strength. The navigators and naturalists of the U.S. Exploring 

 Expedition frequently speak of the rapid outward current passing 

 through the openings of the reefs, especially during the ebbing tide. 

 Dana had noticed the great strength of the tidal currents, and he 

 well explains by their action the great diversity of distribution of 

 material over the bottom of a lagoon or of a barrier reef channel. 



'' There seems to be no question that the action of the sea can cut 

 out the lagoons of barrier reefs and of atolls at the depths at which 

 they have been observed in the Fijis. Although there are individual 

 atolls which show depths of thirty-five to fifty fathoms and even 

 more, these are exceptional depths, which are readily explained as 

 due to other causes than the scouring action of the sea. 



" Admiral Wharton has given an excellent summary of cases 

 showing to what depths the action of the sea in motion may be felt 

 to a sufficient extent to move material at depths of fifty to sixty 

 fathoms. As he justly says, ' The effect [of the action of the waves 

 in an otherwise deep sea over which strong winds are continually 

 blowing] will be to cut down an island more or less rapidly, 

 according to its constitution, to a very considerable depth below the 

 surface, the final result being a perfectly flat bank.' 



"The sections plainly indicate the general flatness of the lagoonsy 

 with a slight inclination in the direction of the flow of the water 

 in the lagoon toward the ship passages leading into the lagoon, and 

 the outline of the islands which have first been cut down by 

 atmospheric agencies show irregularities which disappear finally 

 when they have come within the scope of submarine erosion, 



