184 DALY. 



The following table (I) shows the depths in representati\'e lagoons 

 and on large banks which lack rimming reefs. The mean width of 

 the broader part (not the maximum width) is given in Col. 1. Column 

 2 gives the maximum depth of lagoon or bank. For lagoons, Col. 3 

 gives the mean depth for a considerable area where the water is deepest; 

 for banks, it gives the mean depth on the larger part of the flat top of 

 each bank. In this column the values given are merely estimates, 

 but they assist in giving a mental picture of the submarine relief. 

 Between the ordinary atoll and the reefless bank is a type sometimes 

 called a "drowned atoll," whose rimming reef is submerged because 

 of the periodic killing of its corals. (See page 214.) The depth data 

 for " drowned atolls" are likewise entered in the table. 



Sections of small and middle-sized atolls. 



Figure .5. Peros Banhos, Chagos group. 



Figure 6. Salomon Islands cluster, Chagos group. 



Figure 7. Six Islands cluster, Chagos group. 



Figure 8. North Minerva, 23° 37' S. Lat. and 178° 56' W. Long. Compare 

 Figure 11. 



Figure 9. Wataru, Maldives. 



Figure 10. Section through one of the rare cays of Loai ta "drowned 

 atoll," China Sea. 



Figures 5 to 9 illustrate the rule that the lagoons of small atolls are more 

 filled with detritus than those of larger atolls. Comparison of them with 

 Figures 10, 15, 19, 20, 33, and 34 shows lagoons of "drowned atolls" to be 

 deeper than the lagoons of atolls with reefs awash or reaching the sea surface,, 

 lagoons of nearly equal diameters being compared in each case. 



Uniform scales; vertical scale is 5 times the horizontal scale. Depths in. 

 fathoms. Water is shown in black; rocks, including the reefs, are lined. 



