52 FLORIDA GEOLOGICAL SURVEY-SEVENTH ANNUAL REPORT. 
520 feet. A somewhat harder limestone, containing, however, phosphate pebble. 
540 feet. Limestone similar to that at 520. This limestone is not so light in 
color and does not contain so many shell fragments as the limestone above 
320 feet. 
600 feet. Very fine, siliceous and calcareous sand containing minute black 
phosphate pebble. 
640 feet. Same as 600. 
680 feet. Similar finely powdered material containing, however, less quartz 
sand. 
720 feet. Limestone with slightly brownish color and finely powdered by the 
drill. 
760 feet. Finely powdered calcareous material similar to that at 600 feet. 
800 feet. Light colored limestone consisting of a mass of broken fossils. 
840 feet. Same as at 800 feet. 
880 feet. Same as at 800 feet. 
900 feet. Finely powdered rock including fine quartz sand much like that at 
600 feet. 
950 feet. Limestone consisting of a mass of broken fossils. 
The thickness and succession of formations underlying the peb¬ 
ble phosphate beds as indicated by these records is as follows: 
1. Bone Valley formation. The thickness of this formation is 
not shown by the samples, but the formation is always comparative¬ 
ly thin and when mined is worked to the bottom where it rests upon 
the phosphatic marl known as the “bed rock.” 
2. Beneath the land pebble phosphate beginning with the “bed 
rock” as the term is used in the mining operations, is found a suc¬ 
cession of phosphatic marls extending at Tiger Bay to a depth of 
about 360 feet. At Christina, about 16 miles north of Tiger Bay 
the formation is not more than 100 feet thick, while at Fort Myers 
about 70 miles south of Tiger Bay it is at least 600 feet thick. The 
material throughout this whole thickness, while by no' means uni¬ 
form. apparently represents a single geologic formation which is 
locally variable, the phosphate pebbles which occur throughout the 
whole thickness are black, brown or white in color and are rounded, 
smooth and shiny. The pebble is imbedded in a marl, the prevailing 
color of which is light buff or grayish. The marl is throughout.more 
or less sandy, so much that in some of the samples it becomes almost 
a calcareous sandstone. Locally the material of this marl has be- 
