70 THE FLOOR OF THE OCEAN 



10' I 33*1 SO' 1 172° 



1100 



610 _ 860 675 





1035 

 6* 



MILLE OR MULGRAVE ATOLL 



Scale 



5 10 



Nautical Miles 



X-5 



FIGURE 38. MAP OF MILLE OR MULGRAVE ATOLL. LAND IN SOLID BLACK. 

 DEPTHS IN FATHOMS. 



much more appealing explanation of the break of slope be- 

 tween lagoon floor and reef. According to the better reasoning, 

 the living reefs have grown up from banks, shoals, during a 

 slow, late-Glacial and post-Glacial rise of sealevel all over the 

 world. 



The Glacial Period contained four long successive stages 

 during which major ice-caps were formed on the continents. 

 The Glacial stages were separated by three inter-Glacial stages, 

 times of ameliorated climate. The water of the ice-caps had 

 been evaporated out of the ocean, so that, whenever the ice lay 

 thick on the land, sealevel was lowered everywhere — in max- 

 imum about 300 feet. During each Glacial stage, coral growth 

 was greatly inhibited by the relative coolness of the sea and 

 probably still more by the muddiness of the shore waters, mud- 

 diness being the deadly enemy of the reef-building corals. 

 Lacking defense by living reefs, the old, soft-rock shoals and 



