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 18 
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 moving 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, ete., 
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 Cafiaveral somewhat 
to the eastward of the present shore line of Florida. 
1 Fourth Report British Association, for 1834-1838, p. 11. 
