116 THE TORTUGAS AND FLORIDA REEFS. 



feet above the level of the sea at such points as Anastasia, Merritt's, and Worth Island 



showing ;ill along 



of Florida a very recent formation of shell deh 



breccia very similar to the formation now going on in the lagoons near Venice. This 

 bed of shell breccia was probably deposited after the low backbone of the peninsula, 

 extending from Southern Georgia and Alabama to the northern part of Lake Okecho- 

 bee and the Everglades perhaps, had been raised, and when the peninsula of Florida 

 from the St. John to the eastward was below the level of the sea at a shallow depth. 

 At any rate, it seems plain from recent evidence that no trace of reef-building corals 

 exists on the east coast north of Cape Florida. Mr. Dietz is inclined to look upon 

 the formation of these islands as due to the action of the waves. But there seems 

 to be nowhere, as is well stated by Rogers, any deposit of the kind going on now ; 

 and when such masses of shells are thrown up on beaches, the tendency is strong to 

 consolidate from fragments to the concrete form known as Coquina. 1 The mode of 

 formation does not, however, seem adequately explained by Rogers from the action 

 of currents acting along the coasts. These currents must have flowed over a wide 

 plateau, and have supplied the large amount of food needed for the development of 

 a large and thriving bank of Mollusks and other Invertebrates. As soon as these 

 growing colonies had risen high enough to form banks parallel to the shores, they 

 were in their turn cut off and isolated from the shore by the action of the tides and 

 currents, which must then have begun to deepen the channels intervening between 

 the bars and the mainland. They must also have forced their way across to form 

 the shifting inlets, such as Mosquito Inlet, etc., so characteristic of the channels 

 leading into these inland waters along our whole Southern Atlantic coast. The dip 

 of the Coquina bed to the westward is well shown by the borings of Artesian 

 wells at Palatka. I was informed by the contractor that he met the Coquina beds 

 at a depth of about forty feet, when he reached a mass of clay, which in its turn 

 was underlaid by pebbles resembling the small pebbles found on flats off a rocky 

 shore. Possibly this mass of clay was formed by the silt of the Gulf Stream at 

 a time when it flowed over the low ridge of Central Florida, before that ridge had 

 risen to form a dividing line between the two plateaux, which must have extended, 



the one to the westward much 



while the other undoubtedly extended 



in some localities north of Cape Canaveral somewhat to the eastward of the present 

 shore line of Florida. 



■ 



All this evidence tends to show that the coral reefs had little if anything to do 

 with the building up of the peninsula of Florida north of Cape Florida. The present 



1 Fourth Report, British Association for 1834-38, p. 11. 



