EARLIER TERTIARY (EOCENE AND OLIGOCENE). 741 



"The Ocala limestone consists of a soft, porous light-gray to white limestone which bears 

 a strong lithologic resemblance to the underlying 'Peninsular' limestone, but is distinguished 

 from it by the included fossils. When slightly weathered the rock becomes light yeUow and 

 owing to its granular appearance is often regarded as sandstone. The removal of the calcareous 

 material by the leaching action of underground water leaves a pale-yeUow, more or less incoher- 

 ent sand, containing a small percentage of calcium carbonate. When fresh the Ocala lime- 

 stone is so soft that it is easily broken, but exposed surfaces often become hardened by the 

 deposition of calcium carbonate from the waters which emerge along the outcrop. For this 

 reason the rock frequently appears to be hard and firm. Its porosity and ready solubility 

 permit the formation of numerous underground channels which are sometimes seen at the 

 outcrop and are inferred from the presence of numerous sink holes. The rock contains 

 an abundance of organic remains which are commonly preserved as casts. Nodules and 

 large masses of chert are also common and in some localities a large part of the rock has been 

 silicified." * * * 



"The greatest thickness noted during the recent field investigation was in a sink hole near 

 Ocala, where the formation is exposed to a" depth of about 40 feet without reaching its base." 



Apalachicola group. — The following descriptions are adapted or copied from Matson and 

 Clapp.°*°° In Florida "the Apalachicola group includes a number of beds differing widely in 

 lithological character, though they are recognized by their fossils as integral parts of a single 

 group. While limestones and marls predominate, the group also includes beds of nearly pure 

 sand and clay. The entire period of deposition appears to have been characterized by the 

 accumulation of more or less terrigenous materials, and hence the limestones are usually rendered 

 somewhat impure by an admixture of clay and sand. At certain times the conditions appear 

 to have been especially favorable for the development of organic hfe, and some horizons, such 

 as the Chipola marl member of the Alum Bluff formation and the ' silex bed ' of the Tampa 

 formation, contain very large faunas. 



"Owing to the lithologic variations and widely separated exposures, the exact correlation 

 •of the formations of this group is dependent upon their organic remains. While the paleonto- 

 logical studies, especially those made by Dall, have shed much light upon the stratigraphic 

 relations of the different beds, there are still many points which can not as yet be fully decided. 

 For this reason it seems best to retain the names of various beds and to indicate as far as possible 

 their known relationships. The Apalachicola group is separated into four formations — the 

 Chattahoochee, the Hawthorne, the Tampa, and the Alum Bluff. There is, however, some reason 

 for believing that the first three are, in part at least, synchronous, though exact equivalence is 

 difficult to determine where outcrops are widely scattered and faunal variations are slight. 

 The Alum BWff formation is clearly younger than the Chattahoochee formation, upon which 

 it rests." 



The Hawthorne formation, "according to Dr. E. H. Sellards, is a hght-colored soft, porous 

 hmestone. The original building-stone quarry wliich is located near the station of Grove Park, 

 about 3 miles west of Hawthorne, is now abandoned and is badly overgrown, so that the thickness 

 of this limestone can not well be determined. At the old phosphate mine, which is at least a 

 mile southwest of the stone quarry, the rock is a phosphatic conglomerate. At many locahties 

 the limestones of the Hawthorne formation are silicified, forming bowlders and beds of chert. 

 This is a very common condition in the rock-phosphate region, where these Hmestones rest 

 directly on those belonging to the Vicksburg group. 



"Beneath the phosphatic limestones of the Hawthorne formation are beds of sand, sand- 

 stone, or gravel, which are underlain by several feet of clay. The sand beds at some localities 

 contain iron oxide which forms a coating on the grains of silica. The clays are greenish and 

 locally sufficiently calcareous to be called a marl. The thickness of the Hawthorne formation 

 varies greatly, the maximum amounting to approximately 95 feet. The three members of this 

 formation with their maximum observed thicknesses, according to Dall, consist of greenish 

 clay 70 feet, ferruginous yellow sandstone 4 feet, and phosphate rock 20 feet. The maximum 

 thickness of the Hawthorne formation, as given by the same author, is 125 feet. However, 



