214 



DALY. 



An easier explanation is found in the special weather conditions of 

 this oceanic area. The hurricanes of the South Indian ocean often 

 arise far to the east of the Chagos bank and sweep westward, creating 

 tremendous seas, which attack the bank and stir its muddy surface. 

 The region is also visited annually by more ordinary storms, in number 

 unusual for most tropical seas. Danckelman states that this part of 

 the Indian ocean has an average of 119 days of heavy weather ("Ge- 

 wittertage") every year, while the sea 35-40° farther south has a 

 corresponding average of only 15 days.*^ If the occasional hurricane 

 stirs the mud so thoroughly as to kill off most of the corals, the surf 

 must succeed in cutting down the top of the atoll reef, no longer de- 



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Figure 34A. Turpie bank, north of the Fiji group. This bank is only 

 partly rimmed, yet shows nearly the same depth of water as that in the lagoons 

 of Penguin or Alexa bank (Fig. 34B). Such close agreement, like the flatness 

 of each platform, is difficult to explain on the subsidence theory. Scale, 1: 

 307,000. Depths in fathoms. 



46 See O. Kriimmel, Handbuch der Ozeanographie, Stuttgart, 1, 321 (1907). 

 According to C. Darwin (Coral Reefs. London, 3rd ed.. p. 40 (1889)), the sea 

 is sometimes discolored with sediment washed out of the entrances to the 

 Chagos atolls. On pages 87 and 113 of the same book will be found his classic 

 statements as to the fatal effect of sediment on growing corals. 



