70 FLORIDA STATE GEOLOGICAL SURVEY. 
fossils have been found in a marl overlying phosphate rock which be¬ 
longs to this formation. At various points in the peninsula of Flor¬ 
ida the Hawthorne formation is found resting unconformably upon 
limestone of Vicksburg age, and in the vicinity of Hawthorne thin 
beds of conglomerate occur in the base of the formation. At many 
of the phosphate mines in central Florida the limestones of the 
Hawthorne formation are found overlying either the Ocala limestone 
or the ‘“Peninsular" limestone with an apparent unconformity, which 
has permitted the deposition of sands and some limestone beds along 
channels developed in the upper surface of the Vicksburg formations. 
It should be said, however, that in many .of these cases the materials 
belonging to the Hawthorne formation appear to have been more or 
less disturbed since their deposition, and it is possible that at some 
localities the apparent unconformity may be due to the falling of the 
roofs of caverns developed near the contact of the two formations. 
The relation of the Hawthorne formation to the other members of the 
Apalachicola group has not been determined, but there is no doubt 
that its deposition was in part contemporaneous with the Tampa and 
Chattahoochee formations. In fact, while the absence of paleonto- 
logic information makes it impossible to correlate these formations on 
biologic grounds there is little doubt that they were all deposited 
during an extensive submergence which succeeded the emergence of 
the rocks belonging to the Vicksburg group. On physical grounds, 
therefore, there is good reason for regarding these formations as 
synchronous. 
Lithologic Character:—According to Dr. E. H. Sellards the rock 
at the type locality at Hawthorne is a light-colored, soft, porous lime¬ 
stone. The original building stone quarry, which is located near the 
station of Grove Park, about three miles west of Hawthorne, is now 
abandoned and is badly overgrown, so that the thickness of this lime¬ 
stone cannot 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 localities 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 
limestones rest directly on those belonging to the Vicksburg group. 
Beneath the phosphatic limestones of the Hawthorne formation are 
beds of sand, sandstone, 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. 
Thickness. — The thickness of the Hawthorne formation varies 
greatly, the maximum amounting to approximately ninety-five feet. 
The three members of this formation with their maximum observed 
