,4 Contribution to the Geologic History of the Floridian Plateau. Ill 



Doliurn galea Linn. Tellina radiata Linn. 



Natica canrena Lam. Metis intastriata Say. 



Neverita duplicata Say. Macrocallista maculata Linn. 



Pecten irradians Lam. Chione cancellata Linn. 



Locality: Torch Key, eastern side, along railroad embankment (A. G. Mayer and 

 T. Wayland Vaughan, collectors). 



Siderastrea radians (Pallas). Cardium isocardia Linn. 



Fulgur perversum Linn. Phacoides pennsylvanicus Linn.' 



Dolium galea Linn. Divaricella quadrisculata Orb. 



Cerithium thomasiae Sowerby. Dosinia elegans Conrad.' 



Cerithium littoratum Born. Chione cancellata Linn. 



Modulus modulus Linn. Tagelus divisus Spengler. 



Pecten gibbus Linn. Semele cancellata Orb. 

 ^The two valves are still adherent. 



All of the species are Recent, and the geologic age is Pleistocene. 



The fossils show no attrition, and the two valves of some of the 

 pelecypods are still in their natural position. These fossils must have 

 remained embedded in the material in which they were more or less 

 embedded when alive. In other words, the surrotmding oolite must have 

 originated as a water-laid deposit. 



Mr. Agassiz, in his theory of sands blowing into sounds behind the 

 keys and still preserving the character of wind-blown deposits, could 

 scarcely have had it in mind that the sounds or hollows were filled with 

 water, as it could not be expected that sand blown into water, and 

 deposited through it, would preserve the same structure as if subaerially 

 deposited. 



To summarize the conclusions pointed by the data presented in the 

 foregoing remarks: 



1 . The fossils show that the oolite is a water-laid deposit formed in 



shallow water, a few fathoms, or more probably only a few feet, 

 in depth. 



2. The cross-bedding shows it was formed in areas of moderate 



and variable currents. 



3. The topography shows it was formed on fiats. 



4. The Miami, oolite has been elevated above the water-level a 



sufficient time for it to have suffered considerable denudation; 



while the Key West oolite preserves its original flat surface 



with intact mud cracks. 

 One object in view in collecting bottom samples within the keys 

 was to obtain light on the problem of the origin of the oolites, and the 

 effort had a negative result. A study of the oolites themselves seems to 

 have answered the question. While on Boca Grande Key, on the beach 

 of which oolite occurs, I obtained a suggestion that was perhaps of value. 

 It seems to me that the shells of an oolite grain accumulate around some 

 nucleus by the gentle rolling of that nucleus on a bottom on which 

 calcium carbonate is being precipitated. There is no evidence that 

 oolite is being formed behind the keys east of Bahia Honda, but I think 

 it very likely that it is forming around some of the more westerly keys. 

 Two geological formations of marine origin remain to be discussed: 

 the Lostmans River and Key Largo limestones. The former was de- 

 scribed on page 130; the latter on pp. 130, 131. 

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