P. A. Daly — Problems of the Pacific Islands. 179 



become rimmed with growing reefs that follow the edges of 

 the platforms. These are the atolls and barriers of the Pacific 

 and Indian oceans. 



The exterior location of atoll reefs is illustrated in figs. 20 

 to 25. 



Exceptionally, small colonies have withstood the fatal mud 

 baths of the platform interiors and to-day form the coral knolls 

 of the lagoons. Since these are normally steep-sided and rise 



Figs. 26-29. 



IMT. BUCHAN 























| SH0RE 10 



13 



15 



16 



18 20 



HASTINGS 

 21 20 20 21 20 REEF 20 30 31 30 25 



27 









ill 



P z ± § Sea Miles ? . . ? § 'I Km. 



I 5 9 ll 13 14 15 16 19 18 18 18 19 30 25 32 



TTfTTTmrnTi 

 28 



51 



„ SHORE 



rtV' 9 l9 26 ll 



30 



31 30 3' 



34 32 35 











|29J 





l 



Figs. 26-29. Cross-sections of the Australian shelf, illustrating the super- 

 imposition of the existing coral reefs on a broad platform, which was devel- 

 oped before, and independently of, the growth of those reefs. Water shown 

 in solid black ; rocks, including reefs, are lined. Uniform scales ; vertical 

 scale twelve times the horizontal. 



26. At 13° 10' S. Lat., through the Great Barrier Eeef. 



27. At 16° 35' S. Lat., through the Great Barrier Beef. 



28. At 24° 30' S. Lat. , outside the coral sea. The shallowness of the 

 shelf here is explained by Becent, rapid aggradation, due to the local config- 

 uration of the coast and by a corresponding abundance of sand. 



29. At 24° 45' S. Lat., outside the coral sea. 



from lagoon floors 150 to 250 feet below sea-level, danger of 

 extinction by bottom mud has long been small. Hence many 

 knolls bear luxuriant coral patches. 



The lagoons themselves represent platform areas slightly 

 shallowed by a veneer of post-Glacial detritus, shelly deposit, 



