FLORIDA STATE GEOLOGICAL SURVEY. 
72 
posed in the walls of the sink, which has a depth of about 115 feet. 
Here the greater portion of the section belongs to the Vicksburg 
group, but a phosphatic rock near the top probably represents the 
Hawthorne formation. Another sink which exposes this formation 
is located in section 18, T. 7 S., R. 18 E. At this locality the section 
given by Dali 1 is: 
This place is locally known as “Nigger sink,” and the Vicksburg limestone 
has been reached by a well hole in the center of it. Above the well the lower 
10 feet of the wall of the sink is hidden by talus, but is believed to be clay of a 
greenish-yellow color, 30 feet of which rises above the talus, covered by a 
four-foot layer of firm, hard sand, almost a sandstone, and this by a sandy 
ferruginous layer of clay and gravel containing an oyster, like O. virginica, 
reproduced in chalcedony. This ferruginous layer, which will be referred to 
here under the term ferruginous gravel, seems to appear in many different 
sections, with its oyster and silicified corals. It also occurs in Georgia. Above 
it is a layer 2 feet thick of soft sandstone resembling the phosphatic rock in 
appearance. Covering this is a bed of sand and clay 8 feet thick containing 
fragments of all sizes, from a few pounds to a ton in weight, of the phosphatic 
rock and its large, silicified coral heads. These last, when they appear on the 
surface as around Archer, from the solution of the phosphatic matrix are 
popularly known as “fossil stumps” or “nigger heads.” They are large masses 
of chert or chalcedony, often hollow, retaining on the surface more or less 
obscure indications of the original coral structure. Above this stratum come 
the surface sand and loam, here about 20 feet thick. 
In this sink the well was drilled to limestone of the Vicksburg 
group, but the depth and character of the material penetrated are not 
given. The same writer gives more or less complete descriptions of 
several other sections. 2 One of these is in Newnansville, where the 
clay which immediately overlies the limestones of the Vicksburg 
group has a thickness of seventy feet and is overlain by two feet of 
ferruginous sand, three feet of undescribed material, and eight to 
twenty feet of phosphatic rock. About five miles east of Mixon’s the 
ferruginous sand rests on the Vicksburg group and is overlain by the 
phosphatic bed, and nearer Archer the remnants of the phosphatic 
rock are found resting directly upon the Vicksburg. Occurrences of 
similar phosphatic rock are reported where the railroad crosses the 
Hillsboro River and at Jarves Springs; while at De Leon Springs a 
phosphatic rock is said to be overlain by beds containing Chipola 
fossils. The same phosphatic rock is also reported from Live Oak 
and Lake City, and the ferruginous bed with its silicified oysters is 
known to occur at Levyville and at Magnesia Springs. The following 
sections are given by Dali : 3 
1 Loc. cit. p. 109. 
2 Op. cit. 
3 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey Bull. 84, 
1892, pp. 110-111. 
