446 B. Pumpelly — Time-break between the 



that they have been transported very far. The only light 

 obtained thus far as to the age of the upper part of the plateau 

 is found in extensive areas of residuary fossiliferous angular 

 fragments, representing broken-up siliceous beds. These occur 

 at numerous points on the plateau at altitudes of 230 to 260 

 feet above the sea, and seem to belong below the ferruginous 

 sand with iron ore pebbles. These fragments up to several 

 cubic feet in size, are found covering the surface in areas of 

 many acres in extent, and also imbedded in the underlyin 

 clays. At one locality, which we were accustomed to cal 

 Gasteropod gully, near Roseland plantation, southeast of 

 Bainbridge, the range exposed between the fragments on the 

 surface, and those in the clays in the adjacent gullies is as 

 much as 60 feet or more, although under the circumstances 

 the true relation between the upper and lower fragments is 

 not apparent. Thes3 fragments consist of silicified beach-worn 

 shells which either make up almost the whole rock or are im- 

 bedded in the sandstone. The fossils are of Chipola Miocene 

 Age. Of these Mr. Foerste sends me the following list from 

 his determinations. 



"Ostrea divaricata, var., Pecten Madisonianus Area idonea, 

 Carditamera? protracta, Yenus mercenaria, var., Strigilla ilex- 

 uosa, Mactra subcuneata, Solen ensis, Conus planiceps, Drillia 

 similar to lunata, Melongena similar to subcoronata, Typhis 

 acuticostata, var. typhis similar to gracilis, Turritella gatu- 

 nensis, Turritella with an ornamentation similar to T. acropora, 

 but shell is larger, T.? terebriformis, Solarium bellastriatum, 

 var. Yicksburgense, a moderate variation from the same. 

 Crucibulum auricula var.? imbricatum, Calyptrsea centralis, 

 Crepidula fornicata, Natica floridana, Chlorostoma (Ompha- 

 lius) '? exoletum, Helix adamnis, var. Bulimulus % Balanus ? 



As stated above the surface of the plateau is generally undu- 

 lating. Wherever it has been exposed to cultivation deep 

 gullies have rapidly cut their way back into it. These facts 

 would incline one to look upon the plateau as a Miocene island 

 area covered and levelled up with a much more recent sand 

 formation. The younger sands may however be of Miocene 

 age like those above the Chipola and Ecphora beds at Alum 

 Bluff. And they may have been continuously protected from 

 erosion by the density of vegetation and the porosity of the 

 rocks which permitted the downward drainage, into subter- 

 ranean channels, which is still active throughout the region. 

 This last alternative accords with the view expressed by Mr. 

 A. F. Foerste,* that these sands represent the shoreward ex- 

 tension of the Chipola and Chesapeake formations. 



The evidence for a time break between the Eocene and 

 Chattahoochee Miocene consists in : 



* Chipola Miocene of Bainbridg-e, Ga.. and Alum Bluff, Fla. This Journal, 

 Oct., 1893. 



