42 ■ Bulletin 15 353 



PART II, 



The Oligocene of the Southern United States. 

 General Extent. 



The extent, as now determined, of the Olig^ocene in the 

 Southern States is shown on the map on the opposite page. 



The Vicksburg Kmesfo7ie. North of the large area of Vicks- 

 burg limestone, which passes through Georgia, dips into Florida, 

 and, crossing Alabama and Mississippi, ends in the Vicksburg 

 bluff, are isolated outcrops of the same rock noted by Prof. Harris, 

 Their position in surrounding Eocene recalls the similarly situated 

 Oligocene areas of Ecouen and Montmorency in the Paris basin. 

 That these are remnants that have resisted the erosion which 

 has removed the rest of the original northern extension of 

 the present Vicksburg sheet is more than probable. They indi- 

 cate that the limestone formerly extended at least as far north as 

 Macon and Montgomery and to the north of Jackson. The most 

 western exposure of Vicksburg is north of Harrisonburg, Louis- 

 iana, in the vicinity of Rosefield. 



The southward extension of this limestone, as surface rock,, 

 is not great, since its extent is concealed beneath later deposits 

 and the waters of the Gulf of Mexico, Borings at St. 

 Augustine have shown that the Vicksburg has there a depth of 

 1,066 feet. The indications are that the entire peninsula of 

 Florida rests upon a plateau* of this limestone, which formerly 

 extended continuously to Cuba and the Bahamas, but has since 

 been disse(5led and channeled by the erosive acftion of the Gulf 

 Stream. 



Chattahoochee Ihnestones and clays. The Chattahoochee argil- 

 laceous limestones and clays are chiefly developed in Florida and 

 in southern and southeastern Georgia. They also extend a trifle 

 beyond the western state line of Florida and Alabama. 



*Dall, Bull. U. S. Gevl. Survey, No. 84, p. iSi. 



