.32 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
in this section include, aside from the Vicksburg limestones of Lower Oligocene age, Upper Oligocene formations of the Apalachicola group, Marine Miocene formations, and more or less of Pliocene or later materials since all of these formations occur in position in the adjacent and uneroded high-lands to the northeast. In the course of the decay and lowering of the general land surface there is naturally more or less shifting of material attended probably by the formation of temporary small lakes and streams. It is possible that the conditions thus arising may have been sufficient to account for the mixed condition of the materials, the tendency to stratification in places and other evidence of action by water without the necessity of assuming a complete resubmergence. On this point, however, the writer feels that evidence has not been accumulated to form a final opinion.
FORMATION NAME.
It is thus apparent that the formation contains a mixture of material largely residual from several formations from a early as the Lower Oligocene and as late at least as the Pliocene, fur-ther complicated by subsequent chemical action within the formation itself. The residual material moreover has been reworked and in places transported and redeposited. The term Dunnelhnil formation is suggested for these deposits since they were first found and are best developed in the vicinity of Dunnellon, Florida.
EXPLANATION OF PLATE I.
Fig. I. Phosphate washer for hard rock phosphate in use at pit No. 3, Cummer
Phosphate Company, Alachua County.
Fig. 2. Drill for prospection for hard rock phosphate, in use by the Southern
Phosphate Development Company. The prospect holes are drilled through the phosphate formation to the underlying formation, the Vicksburg Limestone, which is reached at this locality at a depth
of 75 to ioo feet.
Fig. 3. View of incline to pit, in the Croom mine of the Buttgenbach Phosphate
Company.