AGASSIZ: THE FLORIDA ELEVATED EEEF. 55 



Notes upon Specimens. — At Mr. Rhodes's quarry, Cocoanut Grove, is 

 found a liue white oolitic limestone containing occasional small shells. 

 The oolite grains are about half a millimeter in diameter. The oolitic 

 structure can be determined by the eye, though a microscopic examina- 

 tion of a thin section is necessary for details. There is a nucleus usu- 

 ally of calcareous substance of more or less irregular form, apparently a 

 detrital grain, about which have been formed a few rings or a shell of 

 similar substance ; sometimes a radiating fibrous structure is faintly 

 shown between the rings, and also in the rock cement. Small angular 

 grains of quartz are abundant also as nuclei. 1 



Surface specimens obtained in the same region, as far inland as fifteen 

 to twenty-two miles from the coast, show similar composition and struc- 

 ture, though the oolitic character has been somewhat obscured, appar- 

 ently by surface changes. Specimens obtained below the surface, in 

 natural wells and from river banks, show good oolitic composition. This 

 is true as far north as Xew River, and would give the oolite an exten- 

 sion north and south of at least sixty miles ; it is at least thirty miles 

 wide in the vicinity of Cocoanut Grove, and fifteen miles at Xew River. 



Thirty miles north of New River, in the vicinity of Linton, there is a 

 cross-bedded fragmental rock, probably representing the northward ex- 

 tension of the oolite. The quartz material is more abundant, however, 

 and of coarser grain, and the oolitic structure is not common, and the 

 oolite grains are smaller. Specimens from the canal at Linton show 

 oolite interbedded with coquina. Still farther north, about Lake Worth, 

 there is rock resembling that at Linton, with rare traces of oolitic struc- 

 ture. A specimen of a friable rock from Cape Canaveral, which may be 

 homologous, shows quartz predominating and considerably coarser in 

 grain. Traces of oolitic structure are found. Coquina abounds here 

 and to the north. 2 



Contemporaneity of Oolite and Coquina. — The interbedding of coquina 

 and oolite at Linton, the close association of the two rocks observed 



more regularly stratified oolitic rocks are also the remnants of extensive coral 

 beach rocks laid down dipping at a slight angle to the sea (6° to 10°) flanking the 

 keys and flats interspersed between the stretches of the elevated coral reef. Such 

 beach rock as is characteristic of Loggerhead Key, the sea face of Key West 

 (Plates I., V.), and of many other keys. — A. Agassiz. 



1 The oolitic structure described by Mr. Griswold applies in every way to aeo- 

 lian rock blown from a coral reef sand tract. — A. Agassiz. 



2 The presence of quartz particles shows how far inland the shore quartz sands 

 are carried by winds, just as this quartz sand can be detected south of Key Bis- 

 cayne. — A. Agassiz. 



