JR. Pumpelly — Time-break between the Eocene, etc, 445 



Art. LX. — An apparent Time-break between the Eocene 

 and Chattahoochee Miocene in Southwestern Georgia; by 

 Kaphael Pumpelly. 



Through the southwestern part of Georgia and adjacent 

 northern Florida there extends a plateau known as the Red 

 Clay hill region. It has a maximum altitude approximately 

 300 feet above the sea, and an undulating surface, with the 

 main drainage channels cut, with steep cross profiles, to a depth 

 of over 100 feet. 



This plateau is sharply limited on the north by an often 

 steep declivity facing the Eocene flat-land country, and con- 

 sists of Miocene deposits resting on Eocene, both of which dip 

 about 13 feet to the mile to the South. The section along the 

 Flint River where it is cut into the flat-land country, exposes 

 the limestone and siliceous Eocene beds abounding in Yicks- 

 burg fossils. Of these Mr. Foerste writes me, that they form 

 "a varied fauna, including species of Operculina, Orbitoides, 

 many corals, Cidaris, Echinocyamus, Clypeaster, Scutella, 

 Lunulites, Ostrea, Pecten, Amusium, Spondylus, Plicatula, 

 Cardium, Turritella, Vermetus, Xenophora, Xatica, (Ampulina), 

 Cerithium, Strombus, Cyprsea, Cassidaria (Sconsia), Fulgur, 

 Conus and fragments of claws of crabs ; among these species 

 Echinocyamus parous, Eumnus, Scutella Lyelli, Pecten Poul- 

 soni, and unknown species of Pectunculus and Cerithuum may 

 be mentioned as especially characteristic of the Vicksburg 

 horizon in Southwestern Georgia." 



Where the Flint River cuts through the plateau at an altitude 

 of 40 to 50 feet above the sea, it exposes the white calcareous 

 beds of the Chattahoochee group, but without any visible con- 

 tact with the underlying Eocene. As has been shown by Mr. 

 Langdon,* the river bank is occupied by the Chattahoochee 

 formation until its gentle southerly dip brings its upper surface 

 below water, and under the Chipola Miocene group at Alum 

 Bluff. 



The base of the plateau is Chattahoochee. The exposures 

 in sides of deep ravines and freshly eroded gullies in the 

 plateau almost uniformly show only more or less sandy clays, 

 which in the higher parts seem to be more sandy, and contain 

 smooth pebbles of sandy iron-ore, which may be either clastic 

 or concretionary, and also frequent pebbles of quartz, clearly 

 derived from metamorphic schists. These quartz pebbles are 

 often f to If inches long by ^ inch broad, with a thickness of 

 only -^2 to I" inch, and so angular that it is difficult to believe 



*Some Florida Miocene, this Journal, October, 1889. Variations in the Creta- 

 ceous and Tertiary Strata of Alabama, Bull. Geol. Soc. Am., vol. ii, July, 1891. 



Am. Jour. Sci.— Thikd Series, Vol. XLVI, No. 276.— Dec, 1893. 

 31 



