Key Largo Limestone, first 

 named and described by Sanford 

 (1909), represents a typical organic 

 reef composed of jn_ situ , wave re- 

 sistant elements, the most important 

 of which are hermatypic corals. 

 These form the framework of the 

 structure and are responsible for 

 the trapping of large amounts of 

 calcarenite in which they are now 

 embedded (Multer 1977). Hoffmeister 

 and Multer (1964) summarize the 

 spatial distribution, community com- 

 position, chemical composition, and 

 additional qualities of the Key 

 Largo Limestone as follows: 



"The Key Largo is an elevated 

 coral reef of Pleistocene age. Its 

 horizontal extent is now fairly well 

 known by aerial examination and core 

 borings. It underlies Miami Beach 

 in the north, comes to the surface 

 at Soldier Key and is again submer- 

 ged beneath the Miami Oolite from 

 big Pine through Key West. In 

 addition it has recently been found 

 a few feet beneath sea level along 

 the eastern shore of the Florida 

 mainland from Miami southward for at 

 least 40 miles. 



"It varies considerably in 

 thickness throughout. At Key West 

 and Big Pine Key it is at least 180 

 feet thick, at Grassy Key 170 feet, 

 at middle Key Largo 70 feet, and at 

 the northern tip of Key Largo 145 

 feet. Wherever its base has been 

 located it rests on an unconsoli- 

 dated guartz and calcareous sand. 



"Its composition is that of a 

 typical coral reef with large, mas- 

 sive coral heads, many in place, 

 surrounded by smaller coral colo- 

 nies, shells and shell fragments of 

 all sizes of common marine organ- 

 isms. Reef building corals are 

 found from top to near the bottom 

 of the formation, but, in general, 

 are more prolific in the upper two- 



thirds than in the lower third. An 

 indurated calcarenite of varied 

 organic components is probably the 

 most important rock by volume. 



"Probably the dominant coral 

 species of the formation are Mon- 

 tastrea annularis , Diploria clivosa , 

 O. Strigosa , U. labrinthiformis and 

 several species of Porites . In 



addition Acropora cervicornis is 

 prolific at several localities. 

 Practically all the coral species 

 found living today on the Florida 

 reef tract can be recognized in the 

 Key Largo. One notable exception is 

 Acropora palmata . This species, 

 commonly known as the Elkhorn coral , 

 is one of the most prolific in the 

 living reefs and as yet has never 

 been located in the Key Largo. 



"...The great bulk of the Key 

 Largo Limestone is greatly altered 

 and recrystallized. Some excellent 

 specimens of well-preserved corals 

 can be found here. From these it 

 has been determined, on the basis of 

 the Thorium-Uranium ratio that the 

 apparent age of the upper part of 

 the Key Largo Formation is about 

 100,000 years. 



"One of the most interesting 

 types of lithology of the Key Largo 

 is what has been called for want of 

 a better name "holey limestone" . 

 This rock displays an unusual frame- 

 work structure in which numerous 

 large and irregularly shaped holes, 

 which comprise 40 to 60 percent of 

 the total volume, are present. The 

 rock is found chiefly a few feet 

 below sea level and is brought to 

 the surface in large guantities by 

 dredges engaged in making cuts for 

 boat slips and canals. 



"The origin of this rock has 

 posed a difficult problem. Although 

 it is believed to have been formed 

 in more than one way, it is now 



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