L. C. JOHNSON — THE CHATTAHOOCHEE EMBAYMENT. 131 



Defined in a more extended sense, the Chattahoochee embayment will stretch out 

 almost to the basin of Suwanee river, or at least to about the middle of Madison 

 county. The rocks found in this extension present quite another aspect. When 

 collections were first made in this part of Florida a few years ago, the leading type 

 was called the Wakulla formation because it abounds in the vicinity of the springs 

 of 1 hat name. The material was taken out of a deep well two miles southwest of Tal- 

 lahassee. The leading features of this rock were an abundant Hemicardium (species 

 not determined so far as the writer is aware) and the large Orbitulites floridana, to- 

 gether with many land shells. The rocks vary greatly in material ; sometimes a 

 quite pure limestone, at other places, or in other layers, aluminous and silicious. The 

 collection from the well shows a good limestone, with calcite filling the cavities left 

 by removal of the suhstance of the shells, and with some lumps or streaks of chert ; 

 the deposit was said to be 80 feet thick. Two miles northwestward and one mile 

 northward there are hills fifty to one hundred feet higher, covered with Lafayette 

 sand. 



The excavation at the Saxton mine, 3^ miles west of the court-house in Tallahas- 

 see, reaches this rock, and is interesting because showing that here again its surface 



is the place of phosphates. The section here is as follows : 



Feet. 



1 . Soil and subsoil (Lafayette sand) 6-10 



•_'. ( heenish plastic clay ; stands high heat ; has a few nodules of hard phos- 

 phate ; of doubtful genesis 1" 



:;. A compact, friable sand, very white and pure ; of doubtful genesis 6-9 



■i. Dirty clay, with nodules of phosphate and rotten leaves; also of doubtful 



genesis 3 



5. Sandy clay, colored by organic matter, leaving fragments of fossils all 



leached away except a chalcedonized Ostrea li 



(i. Whitish sandy clay, phosphatic, with lumps of pure white clay 8 



7. Yellowish white clay, phosphatic, sandy, with peculiar irregular masses of 



very hard phosphate* 12 



s. Bed rock, dug into only 2 feet ; soft, pure limestone without fossils, corre- 

 sponding with first rock struck in well l' miles southwest and 50-100 feet 

 lower; fossils identified with those of the Wakulla beds; similar to 

 those of Weelaunee and Lloyds 



In this part of Florida the great springs or - rises" begin near the coast, ami far- 

 ther back in the higher ground numerous sinks ami lakes occur. This is undoubt- 

 edly because the strong, insoluble sandy or aluminous limestones thin out, as do 

 the overlying impervious clays, so thai there is nothing to prevent infiltration of 

 surface waters, and thus the formation of sinks and subterranean rivers in the 



porous lime-tones of tl Ider formations. When the sinks or outlets are stopped, 



or partially so,lakesand ponds, or at least funnel-shaped depressions take their places. 



An actual section taken where (lie later rock and the superficial Covering are sulli- 

 Ciently thick to prevent sinks will illustrate the relation. A deep excavation at 

 Weelaunee, Jefferson county, Florida (sections :;.". and 36, township 1 south, range 

 I east), gives the following succession : 



♦ The majrix of 1 iber7 i said to run IG% per cent and th« rough, hard nodules 80 per cent of 



phosphate "i linv 



