68 THREE CRUISES OF THE " BLAKE." 



southern Georgia and Alabama to the northern part of Lake 

 Okeechobee and the Everglades, had been raised, and when the 

 peninsula of Florida from the St. John's 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.^ The mode of formation does not, 

 however, seem adequately accounted for by the action of cur- 

 rents movino" 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 thriving bank of mol- 

 lusks and other invertebrates. As soon as these growing colo- 

 nies 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 be- 

 gun to deepen the channels intervening between the bars and 

 the mainland. They must also have forced their way across the 

 banks to form the shifting inlets, such as Mosquito Inlet, etc., 

 so characteristic of the channels leading into the inland waters 

 along our whole Southern Atlantic coast. The dip of the co- 

 quina bed to the westward is well shown by the borings of arte- 

 sian 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, one of which must have extended to 

 the westward much as at present, while the other undoubtedly 

 extended in some localities north of Cape Canaveral somewhat 

 to the eastward of the present shore line of Florida. 



1 Fourth Report British Association, for 1834-1838, p. 11. 



