160 W. II. Ball— Geology of Florida. 



tain their outward form, but are usually mere shells with an 

 interior of botryoidnl chalcedony, often of great beauty. The 

 discovery here of Ecphora quadricostata by Dr. R. E. C. Stearns 

 in 1869 (as pointed out in Science, vol. vi, p. 82, July 31, 1885) 

 indicates the Miocene age of the rock: a suggestion which 

 Heilprin has confirmed by his stud} 7, of the silicified fossils col- 

 lected here in 1885-86. The stratum affording these fossils is 

 not limited to this locality. Conrad found it nine miles up the 

 Hillsborough river which is fourteen miles or so to the north- 

 ward and eastward from Ballast Point, and I am informed that 

 the silicified fossils occur at various intermediate points along 

 the bay shore. I found the same rock and fossils on Six Mile 

 Creek at the head of navigation, near Orient station, about six 

 miles to the eastward of Tampa, on the South Florida railway. 



The fossils are chiefly marine, but there is a certain admix- 

 ture of landshells which becomes more pronounced toward the 

 top of the bed, indicating a gradual increase of the adjacent 

 land area during the deposition of the bed. Finalty, on the 

 upper surface in some places nothing but landshells are found, 

 showing that, at last, it became dry land at least in certain 

 spots. 



These landshells are all of extinct species allied more nearly 

 to those of the West Indies than to the present fauna of the 

 Southern States. A small bulimoid shell has been, I think 

 incorrectly, referred to the Pacific genus Partula, which it 

 somewhat resembles, as observed by Conrad forty years ago. 

 But it is probabl} 7 more nearly related to certain recent Bulimi 

 of the northern Mexican and South American faunae. 



Above the stratum above described is a layer, from a foot 

 and a half to ten feet thick, of limestone free from silex and 

 pretty uniform in character. The fossils are mostlj 7 represented 

 by external molds; but a few, and particularly an orbitolite 

 described by Conrad, and probably identical with one now liv- 

 ing at moderate depths on the Floridian coast, retain their shell 

 structure. Some of the fossils in the lower stratum appear 

 again in this one, but most of the species seem different and 

 there is a notable absence of the large corals so abundant in the 

 older layer. There are more species which seem to be repre- 

 sented in a living state in the present fauna. 



This rock underlies the town of Tampa where wells are dug 

 through it, and water obtained at a depth of ten feet or less. 

 It is probable that the more compact cherty stratum underlies 

 it here and forms a water table. The same rock occurs seven 

 miles northeast of Tampa in wells, and also on land belonging 

 to Mr. Lapenotiere of Tampa (S.EJ Sect. 14, T. 29 R.19), near 

 Orient station. Its upper surface is about fourteen feet above 

 Six- Mile Creek near by, and about twenty-five feet above the 



