CORALS AND CORAL, REEFS— VATJGHAF. 



231 



with considerable exactness. Its surface outcrop has been mapped in 

 Georgia and Florida, and well borings have revealed its presence 

 under younger formations in west Florida at Panama City, and in 

 peninsular Florida at Tampa, Key West, Key Vaca, and Palm 

 Beach. The limestone is largely composed of the remains of myriads 

 of Nummulites and orbitoidal Foraminifera, many Bryozoa, and 

 some mollusks and echinoids, with which there seems to be an unde- 

 termined proportion of chemically precipitated calcium carbonate 

 and some terrigenous material. Corals are everywhere rare and as 

 a rule are absent. The organisms occurring in the formation are 



Fig. 12. — Profiles across continental shelf, east side of Australia. The lati- 

 tude AT THE INTERSECTION OF EACH PROFILE WITH THE SHORE LINE IS FOLLOWED BY 



the statement of the direction of the profile from the shore. 



South of the southern end of the Great Barrier Reef. 



1. From shore east of Leading Hill, S. Lat. 25° 26' 15", South 82° East. 



2. From base of Sandy Cape, S. Lat. 24° 53' 40", North 68° East. 



3. From Toowong Hill, S. Lat. 24° 22' 4", North 45° East, passing between Lady 

 Elliot and Lady Musgrove islands. 



Across the Great Barrier Reef. 



4. From Rodd Peninsula, S. Lat. 24° 0' 0", North 50° East. 



5. From Georges Point, Hinchinbrook Island, S. Lat. 18° 25' 40", North 72° 32' 



East. 



characteristic of tropical shoal water, 50 fathoms or less in depth; 

 and, as the 100-fathom curve delimits the submerged border of the 

 Coastal Plain, it is evident that the Floridian Plateau has been a 

 part of the Coastal Plain and has had essentially its present outline 

 since late Eocene time, before the formation of the oldest Chat- 

 tahoochee reef, which was therefore superposed on a subsiding plat- 

 form not produced by corals. The geologic history of the Floridian 

 Plateau shows that each successive development of Tertiary reefs 

 was on an antecedent platform which was formed by agencies not 

 dependent on the presence of coral reefs, and in all instances the 

 volume of coral as compared with material from other sources is 



