SECOND ANNUM, REPORT—STRATIGRAPHIC GEOLOGY. 
69 
“Grand Gulf and Lafayette formation/’ The major portion of the 
discussion, however, deals with the conditions of sedimentation during 
the deposition of the rocks belonging to the various groups. 
In 1892 Dali 1 divided the formations here called Apalachicola group 
into two groups, retaining the name Chattahoochee group for the 
limestones and marls which are extensively developed in the north- 
central part of the peninsula, and employing the name Tampa group 
to include the beds which he called Chipola marl. Alum Bluff sands, 
Sopchoppy limestone, Tampa limestone and Tampa silex bed. In his 
later paper on the Tertiary faunas of Florida, Dali places the “silex 
bed” at Tampa in his Chattahoochee group. The discovery of the 
characteristic species of the genus Orthaulax in the basal portion of 
the Chattahoochee formation led to this change in the correlation. 
HAWTHORNE FORMATION. 
In 1892 Dali 2 described, under the name of Hawthorne beds, some 
limestones, sands and clays, extensively exposed in the interior of 
Florida, which had been observed by L. C. Johnson. These beds are 
here designated the Hawthorne formation. At the time of the pub¬ 
lication of Dali's report the Hawthorne formation was being quarried 
and had aroused considerable interest because of the presence of phos¬ 
phoric acid in the rock. The formation consists of clays, sands and 
phosphatic limestones and lies stratigraphically between the lime¬ 
stones of the Vicksburg group and the Alum Bluff formation. 
Stratigraphic Position:—The stratigraphic relation of the Haw¬ 
thorne formation to the underlying rocks of the Vicksburg group has 
been observed at several localities in the interior of the peninsula. 
From what is said concerning the geologic history, it is apparent that 
the deposition of the Vicksburg group was followed by a widespread 
emergence of the land which permitted extensive erosion and the 
formation oi hills and valleys. There is no doubt that this emergence 
and consequent erosion affected the central part of the peninsula, 
where the Hawthorne formation is well exposed, for this formation 
rests uncomformably upon either the Ocala or the “Peninsular” lime¬ 
stone at many localities. This relation is emphasized by the lithologic 
character of the beds, for there is an abrupt change from the soft fine¬ 
grained limestones of the Vicksburg group to the clays, sands and 
phosphatic limestones of the Hawthorne formation. The relation of 
the Hawthorne formation to the Alum Bluff formation has not yet 
been accurately determined, though, at De Leon Springs, Chipola 
1 Dali, Wm. H., The Neocene of North America, Bull. U. S. Geol. Survey 
No. 84, 1892, pp. 105-123. 
2 Dali, Wm. H. Neocene of North America, U. S. Geol. Survey, Bull. 84, 
1892, pp. 107, et seq. 
