72 cushman: cretaceous age of limestones 



the Lower Cretaceous stands 35 feet above present sea level, 

 for the conical Orbitolina appears in the well borings 115 feet be- 

 low the surface. From similar data it appears to be 33 feet below 

 sea level at Anthony and less than 100 feet below sea level at 

 Eustis. 



At other locahties, it is 400 feet below sea level at St. Augustine, 

 820-845 feet at Jacksonville, 500 feet at Tiger Bay, and 1,248 

 feet at Marathon. Assuming an even rate of slope and that 

 the conical Orbitolina is confined to a single horizon, this gives a 

 dip southward from Apopka to Tiger Bay of about 9 feet to the 

 mile and from Apopka northeastward to St. Augustine of about 

 6 feet to the mile. A low anticline is thus indicated with its 

 center somewhere in the general region of Apopka. 



On the upper surface of this Lower Cretaceous Umestone the 

 upper Eocene is represented by the Ocala limestone and in part 

 at least by the Claiborne. The borings indicate that this contact 

 is unconformable, because there is no Upper Cretaceous present 

 in any of the well samples that were examined. This may be 

 due to deposition and subsequent erosion or to the area being a 

 land mass at this time. As the Washita, or upper group of the 

 Lower Cretaceous, is unrepresented so far as can be seen, this 

 group, if deposited, may have been eroded during Upper 

 Cretaceous time while the whole area was elevated to a slight 

 degree, the elevation having taken place, as in other regions, 

 at the end of Lower Cretaceous time. The structure indicates 

 this possibility rather than that the whole series was deposited 

 and subsequently was entirely removed by erosion. It seems 

 then that the area must have been a land mass during Upper 

 Cretaceous and early Eocene time. 



The Ocala and Claiborne are not represented, as far as the 

 samples show, at Apopka and this area may have been an island 

 during the deposition of the Ocala. 



Where the typical Ocala is developed it seems to be only about 

 40 feet thick instead of the much greater thickness usually 

 assigned to it. The fossils of the Ocala are brought up from 

 lower levels but are evidently specimens that have dropped 

 down from higher levels during the drilling. A bed of peculiar 



