88 FLORIDA GEOLOGICAL SURVEY THIRD ANNUAL REPORT.
exceeding i9o feet, while at Melbourne Beach, 150' miles south of St. Augustine, its depth in one well was found to be 221 feet.
Passing to the south from this point the Vicksburg dips rapidly. At Palm Beach, IOO miles farther south, this limestone was reached at a depth of approximately i,ooo feet, *a dip of about 750 feet in ioo miles or 72 feet per mile. The Vicksburg was not reached in a well 700 feet deep drilled by the Florida East Coast Railway Company at Marathon Key, 15 miles south of Palm Beach.T
At Key West, however, the formation is believed to have been Reached at a depth of 700 feet."
It is thus seen that the Vicksburg forms a broad arch extending from central Florida to the Atlantic Ocean. St. Augustine lies near the north slope of this arch, while Melbourne, as nearly as can be determined, lies near the south slope. On either sie of :the arch the limestone dips at a moderate rate. On the north side of the arch, the maximum depth recorded in Florida is 500 feet, Passing to the south a maximum of approximately I,OOO feet is recorded at Palm Beach. While the occurrence of this formation is thus known in a general way the data are as yet imperfect.
In view of the importance of the Vicksburg as an artesian water reservoir the depth at which it is to be expected is a matter ,of very great importance and it is to be hoped that well drillers will find it possible to keep accurately labeled well samples in order .to determine more definitely the distribution of this formation.
APALACHICOLA GROUP.
The Apalachicola group of formations is of a much less uniform 'character than fthe Vicksburg and is also of less importance in connection with the water supply. A full description of this group of formations will be found in the preceding Annual Report of
-this Survey, pp. 67-1o6.
The formations which make up the Apalachicola group include the Chattahoochee and Alum, Bluff formations, well exposed along the Apalachicola River; the Hawthorne formation in central Florida; and the Tampa formation in southern Florida. The relative position of three of these, the Chattahoochee, the Hawthorne and the Tampa formations has not been- definitely determined, and they may be largely contemporaneous. The Alum Bluff formation lies above the Chattahoochee formation., The limestone of this group consists largely of impure clayey material which upon decay
*Darton, N. H.;, Amer. Jeurn. Sci. (3) X LI, p. IO5-6, 189I.
t'Florida Geol. Survey. Second Annual "Report, p. ao6; 190o9.
t Hovey, B. 0. Mus. Comp. Zool.'Bull. XXVIII, .pp. 65-9I, 1896: