Coral Reefs and Islands. 289 



Those having channels are mostly over ten miles in length. 

 A list of them is here given with their sizes, and also the 

 proportion of the reef around the lagoon which is under water 

 above third tide, and bare at low tide, a feature of much 

 interest in this connection. 



JHllice Group. — Depeyster's : 6x6 m. ; three fourths of 

 the encircling reef bare. Ellice's : 9 x 5 m. ; three fourths 

 bare. 



Gilbert Group. — Apia: 17x7 m. ; half bare. Tarawa: 

 21x9 m. ; half bare. Taritari : 18 X 11 m. two thirds bare 

 Apamama : 12x5 m. ; half bare. Taputeuea ; west side 

 mostly submerged, 



Marshall Islands (northern). — Pescadores : 10 x 8 m. ; 

 four fifths bare. Korsakoff: 26 m. ; four-fifths bare. 



Paumotus. — Peacock ; 15x7 m.; nearly all wooded. 

 Manhii : 13x5 m. ; nearly all wooded. Raraka : 6 x 9 m* ; 

 three fourths wooded. Vincennes : 13 x 9 m. ; mostly wooded. 

 Aratica : 18 x11m.; three fifths bare, Tiokea : 18 x 4 m. ; 

 two thirds wooded. Kruesenstern's : 16 x 10 m. ; mostly 

 wooded. Dean's (or Nairsa): 53 x 18 m.; half or more 

 bare. 



g. The absence of open channels in so large a proportion of 

 lagoons, and especially in lagoons of the smaller atolls, appears 

 to be fatal to the abrasion-solution theory. The method of 

 enlarging atolls through currents and solution can act only 

 feebly, if at all, where waters have no free outlet ; and this is 

 eminently so with the smaller atolls which have been assumed 

 by the theory to be most favourable in purity of water and in 

 abundant life for progress ; if the small cannot grow, the 

 large lagoons cannot be made from them by the proposed 

 method. 



Reverse the method, letting the large precede the small (as 

 under the subsidence theory), and then we have a consistent 

 order of events. We have large atoll reefs with several 

 large entrances (like the great barrier- reef about a high island 

 in this and other respects) gradually contracting, and the 

 entrances concurrently narrowing through the growing corals 

 and the consolidating debris, in spite of the efforts of abrasion 

 and solution to keep them open and make them deeper ; and, 

 afterwards, the atoll becoming still smaller until the entrances 

 close up; and, finally, the lagoon-basin is reduced to a dry 

 depression with nothing of the old sea-water remaining except, 

 perhaps, some of its gypsum. 



h. Instead of small lagoons having the purest waters, the 

 reverse is most decidedly and manifestly the fact, and this 



