AGASSIZ: THE FLORIDA ELEVATED REEF. 55 
Notes upon Specimens. — At Mr. Rhodes's guarry, Cocoanut Grove, is 
found a fine white odlitic limestone containing occasional small shells. 
The oólite grains are about half a millimeter in diameter. Тһе odlitic 
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 caloareous 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. 
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 oólitic character has been somewhat obscured, appar- 
ently by surface changes. Specimens obtained below the surface, in 
natural wells and from river banks, show good odlitic composition. This 
is true as far north as New River, and would give the oólite 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 New River. 
Thirty miles north of New River, in the vicinity of Linton, there is à 
cross-bedded fragmental rock, probably representing the northward ex- 
tension of the odlite. The quartz material is more abundant, however, 
and of coarser grain, and the oólitio structure is not common, and the 
oölite grains are smaller. Specimens from the canal at Linton show 
oólite interbedded with coquina. Still farther north, about Lake Worth, 
there is rock resembling that at Linton, with rare traces of oólitio 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 odlitic structure are found. Coquina abounds here 
and to the north.? 
Contemporaneity of Očlite and Coquina. — The interbedding of coquina 
and oólite at Linton, the close association of the two rocks observed 
more regularly stratified oólitic 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 oólitie structure described by Mr. Griswold applies in every way to mo- 
lian rock blown from a coral reef sand tract. — A. AGASSIZ. 
? 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. 
