130 PROCEEDINGS OF WASHINGTON MEETING. 



A section in the vicinity (on Sweetwater creek) where phosphate beds occur in 



or above this calcareous soft sandy rock well displays the relation of the members 



in this part of the Chattahoochee embayment : 



Feet. 



1. Columbia sands of river origin ; variable in thickness on account of ero- 



sion ; wells at top of ridge give 20 



2. Alum bluff or Chipola marl ; at this point less than *15 



3. Aspalaga marl;f pectens and oysters in gray calcareous compact sand, 



with darker clay at base 20-40 



4. Aspalaga phase of Chattahoochee formation, or the upper layer extending 



eastward over high lands of Gadsden county; fossiliferous ; estimated 



to be " 30 



5. Lower portion of Chattahoochee formation, generally without fossils; 



more calcareous than number 4 ; calcite in cavities ±40 



6. Place of supposed underlying Vicksburg rocks not seen on the river, south 



of Port Jackson, above the mouth of Flint river 



In this section a thin layer of another variety of sands and clays appears, cover- 

 ing the gray sandy limestone of the pecten-bearing beds and covering the peculiar 

 phosphates of this region. It is doubtless an overlap from Alum bluff of the Chip- 

 ola deposit. It may be traced westward and northwestward into Alabama, on 

 the waters of Yellow river ; but eastward it stretches little beyond Ocklocknee 

 river, after crossing which it becomes lost beneath the later formations on Lost 

 creek and Sopchoppy river. The overlying beds (number 3 of the section) extend 

 up Ocklocknee and Little rivers some distance, and still further eastward into south- 

 western Leon county and the northwestern part of Wakulla county. Between 

 Alum bluff and the Gulf the formations and their relative proportions have not 

 yet been determined. 



Thus, a great part of Jackson county, as well as all of Calhoun, Gadsden, Liberty, 

 and Franklin, with half of Wakulla and the southwestern part of Leon counties. 

 Florida, constitute the Chattahoochee embayment in its most restricted sense. 



In addition to the geologic structure, there are superficial characteristics by 

 which the embayment may generally be recognize I : < didsden county has very much 

 the appearance of the high, rolling pine lands, its natural forest covering being a 

 mixture of oak and hickory, which prevails in the adjoining state- of Alabama and 

 Georgia. It abounds in springs and running streams ; there are no lakes, and none 

 of the sinks so common in other parts of Florida. In all this more restricted em- 

 bayment the lakes, springs, and sinks prevailing in the eastern portions of middle 

 Florida form no part of the topography : because, first, the most soluble and cav- 

 ernous rock of the region (the Vicksburg limestone) lies deep beneath the surface. 

 probably little, if any, above tide ; second, the impure limestones are little soluble ; 

 and, third, the later beds are of great thickness. 



*This deposit runs southeastward to Ocklocknee ami southward to tin' mouth of the river, and 

 westward and northwestward to Alabama, with a thickness of I i el 



fThe phosphates are in or over this deposit. 



I It is estimated, from observations at Aspalaga and Chattahoochee and other places north of Rock 

 bluff that the thickness "1 these two exceeds 100 feet. 



