28 2£cGee — Southern Extension of Appomattox Formation. 



Geographic Distribution. 



The areal distribution of the Appomattox formation may 

 be stated either simply and easily in terms of original deposi- 

 tion, or in greater detail and with more difficulty in terms of 

 present outcrops. 



In general distribution, the formation is known to expand 

 and thicken southward from a few thin beds occupying a nar- 

 row belt on Potomac creek, a few miles north of the Rappa- 

 hannock, to a thick deposit forming a terrane forty or fifty 

 miles wide on the Roanoke ; to extend thence southward, in a 

 broad zone at first widening but afterward narrowing with the 

 encroachment of the overlapping coast sands upon its area, 

 quite across the Carolinas; to form the most conspicuous ter- 

 rane of central Georgia, where it stretches from the fall-line to 

 the inland margin of the coast sands all the way from the 

 Savannah to the Chattahoochee ; to again expand greatly in 

 Alabama with the contraction of the overlying coast sands 

 until it forms an essentially continuous terrane stretching from 

 the fall-line at Montgomery and Tuscaloosa to within half a 

 dozen miles of the Gulf in thesouth western corner of the state ; 

 and to maintain this enormous width in Mississippi, where 

 it extends southward from the Paleozoic area in the extreme 

 northeastern corner of the state to within twenty miles of the 

 Gulf on Pearl River and westward to within fifty miles of the 

 Mississippi, to be in part overlain and in part replaced by the 

 local phases of the more recent Columbia formation developed 

 on Gulf and river. This field of fully 50,000 square miles is 

 that over which the Appomattox has been traced in thousands 

 of exposures, and in which it generally forms the prevailing 

 terrane. 



If the direct observation be supplemented by legitimate and 

 necessary inference, the formation must be so extended as to 

 bridge the valleys from which it has been degraded, and to 

 stretch beneath the various phases of the Columbia formation 

 well toward the Atlantic and Gulf coasts — though its seaward 

 extension is doubtless aberrant in composition and structure, 

 particularly in Florida, where it merges with the continuous 

 series of off-shore deposits of the Neozoic which combine to 

 form the great submarine shelf fringing the continent on the 

 east and south. With this legitimate extension, the field of 

 the formation becomes essentially coextensive with the Coastal 

 Plain of the Atlantic and Eastern Gulf slopes (exclusive of a 

 part of Florida) and assumes an area of 250,000 or 300,000 

 square miles. Over the whole of this vast area the Appomat- 

 tox formation must have stretched ; and over the greater part 

 of this area it must maintain the wonderfully uniform charac- 

 teristics of composition and structure exhibited to-day by its 

 stream-carved remnants. 



