A Contribution to the Geologic History of the Floridian Plateau. 1 75 



Vaughan published the next opinion on the origin of the oolite. 1 

 According to him it was formed as a water-laid deposit, probably behind 

 a seaward barrier. He states: 



The reasons for this opinion are that numerous marine fossils are found in 

 the oolitic material, the two valves of bivalve mollusks arc frequently in place, 

 showing no damage by attrition, and fossil corals which exhibit no indication of 

 having been rolled or waterworn were found. The marine fossils found in the oolite 

 had evidently lived in the water during the formation of the oolite. On the 

 surface of Big Pine Key original mud cracks formed by desiccation were observed 

 and photographed. 



The last published opinion is that of Sanford, who says: 



The characteristics of the calcareous sands and marls accumulating about 

 the keys and in the Bay of Florida, and the distribution, topographic relief, bed- 

 ding, contained fossils, and structure of the Key West and Miami oolites indicate 

 that the latter were limy muds, with a varying proportion of lime sand and a little 

 quartz sand, which accumulated on the bottom of shallow bays or lagoons, where 

 in places the water was relatively still, in places agitated by waves and currents 

 strong enough to build up and level off banks and bars. (Florida Geol. Surv.. 2 d 

 Ann. Report, p. 222, 1910.) 



Two theories have been proposed for the origin of the Florida oolites, 

 viz: (1) that of Alexander Agassiz, who considered that the deposits 

 were of aeolian origin and were made in a "huge shallow sink"; and (2) 

 that of Louis Agassiz, which considered them of aqueous origin. 



In the following account an attempt will be made to assemble the 

 data bearing on these two theories. 



The macroscopic and microscopic structure of the oolite granules 

 shows them to be composed of concentric shells of calcareous substance 

 accumulated around a nucleus in some instances calcareous, in others 

 siliceous. This structure is characteristic of concretions, but the problem 

 of the origins of concretions is raised, and a definite answer is not obtained 

 as to whether the material is of subaqueous or subaerial origin. However, 

 it may be mentioned that the specimens I collected on Cat and Gun keys,' 

 Bahamas, distinctly showed their detrital nature, while the typical 

 Miami and Key West oolites are distinctly not detrital. But as I did not 

 visit a great number of the Bahaman Islands and have seen none of the 

 Bermudas, I have not the necessary information for a general comparison. 



The topography of the surface of the Floridian oolites is not of 

 criterional value, as gentle undulations may be produced under the water 

 or the air, or by slight folding. Here again, however, the flat upper 

 surface of the Key West oolite is more suggestive of water-laid than wind- 

 blown deposits. 



The strong cross-bedding of the Miami oolite has been mentioned 

 in the quotation from Griswold. This has been interpreted by Mr. 

 Agassiz as evidence of aeolian action, and it is stated by Griswold that 

 as evidence it is not decisive. 



In order to illustrate bedding presumably due to wave and aeolian 

 action, separate or combined, a series of photographic illustrations are 

 introduced. Plate 13, fig. a, illustrates an exposure on Gun Key, Ba- 



1 Carnegie Institution of Washington, Year Book No. 7, p. 133, 1909. 



