THE FLORIDA REEFS. 55 



so-called coral breccia (Fig. 36), and the different grades of 

 oolitic ( Fig. 37 ) or compact limestone characteristic of the recent 

 reef formation. 



The coral boulders are the remnants of huge masses of as- 

 ti-eans and mseandrinas, and similar species of corals. The 

 broken fragments of corals come from the different species of 

 branching madrepores and porites or the smaller masses, such as 

 Manicina, Agaricia, and the like ; while the fragments of shells, 

 etc., are derived from the limestone carcasses of the hosts of in- 

 vertebrates which once lived on the active coral reef. The bor- 

 ing mollusks, annelids, and sponges have little by little riddled 

 masses of corals with their burrows, weakening them to such an 

 extent that the breakers pounding upon the exposed sea-faces 

 of the reef break off larger or smaller masses ; these are then 

 heaped up and ground together to form either the top of the 

 reef proper or the inner keys, as just described. 



Of course it can hardly be expected that, with all this pound- 

 ing and grinding and constant rehandling of the material which 

 goes to make the limestone rock of the keys, many animal re- 

 mains should be preserved intact. In fact, with the exception 

 of fragments of the stouter shells of some of the mollusks or 

 tubes of anneHds and the like, there are but few organic remains 

 to be found. 



Corallines, or limestone algae, also play a most important part 

 in the formation of keys. They grow in great abundance upon 

 flats and upon the dead fields of corals which have reached the 

 surface of the sea ; theii* joints are easily recognized in the com- 

 ponents of the coral sand of many a Florida key. Nowhere else 

 along the reef or the line of the keys do we find indications that 

 the highest elevation of the land is due to any causes except 

 those now acting in the formation of the keys. There is not 

 a single point so high that it cannot be reached by the waves in 

 severe storms, or the elevation of which cannot be traced to the 

 action of the tides and winds upon the material of the shore lines. 



All naturalists who have visited the Florida reefs have felt the 

 difficulty of applying Darwin's theory of reef formation to the 

 peculiar conditions existing along the Straits of Florida. Agas- 

 siz, Le Conte, and E. B. Hunt have each in succession attempted 



