SUBMARINE MOUNTAINS 73 



MAIN CORAL CORAL CORAL MAIN 



REEF KNOLL KNOLL KNOLL REEF SEALEVEL 



fllflfilii^f AT0LL FORMED IN LAST INTERGLACIAL STAGE MffiKUmMvh 



SEALS vt IS 

 I SEALEVEL SOMEWHAT LOtVEffEO IN LAST GLACIAL STAGE \ vg 



^ J % REEFS DEAD AND PARTLY ERODED BY WAVES |pg|f|§i§||| 



SEAL EVEL S 

 -« N0 t — _ 



SEALEVEL JUST AETEff MAXIMUM 01= GLACIATION 



^ REEFS DESTROYED DEGLACIATION BEGINNING. 

 1////////////////S SOME CORAL COLONIES (DOTS). 



iSEALEVEL SOMEWHAT BISEN IN LATE GLACIAL TIME ^ SEALEVELS 

 -j — — — -^- NO. I 



/ %M, NEW REEFS GROWN UP IN LATE GLACIAL TIME 



Existing 

 sealevel 



1 1 ^ m NO S - 



^^^^P LIVING REEFS OF THE PRESENT TIME //f/ 



FIGURE 41. SECTIONS ILLUSTRATING THE GLACIAL-CONTROL THEORY OF THE 

 LIVING CORAL REEFS. REEF IN SOLID BLACK; PLATFORM IN DIAGONAL SHADING. 



just right to match the height of the wall-like reefs above the 

 lagoon floors. 



Second, the relative merits of the two theories can be tested 

 by the logs of bore-holes sunk in appropriate places. Darwin 

 and Dana regarded the Great Barrier Reef of Australia and 

 associated lagoon, each 1200 miles long, as furnishing the 

 grandest example of subsidence. Now, two borings have been 

 made through coral rock situated well inside the Barrier and 

 also far from the main shore of Australia. See Figure 42. Ac- 

 cording to the subsidence theory, coral rock should have been 

 found in each hole at depths far exceeding that of 300 feet 

 below sealevel. Figure 35 gives, in summary, the logs of the 

 two borings. At Michaelmas Cay the coral continues down 

 to the depth of 237 feet; at Heron Island, to the 288-foot level, 

 where a bed of pure quartz sand was found. Neither depth 



