McGee — Southern Extension of Appomattox Formation. 17 



deposited in a sheet of variable thickness, ranging from a 

 trilling veneer near the fall-line and at high levels to a con- 

 siderable bed of stratified deposits toward the coast. In the 

 Southern Atlantic and Eastern Gulf slopes, the formation in 

 like manner consists commonly of two principal phases and 

 several local varieties ; yet all are connected by stratigraphic 

 continuity : In North Carolina the relations displayed in the 

 District of Columbia are maintained, save that the interfluvial 

 phase becomes progressively more and more sandy in crossing 

 the state from north to south, and finally passes into the 

 essentially continuous veneer of sandy loam or fine sand com- 

 pletely covering the seaward portion of the Coastal Plain from 

 the Neuse river to Mobile bay ; in South Carolina the fluvial 

 phase becomes transformed into a sandy or silty loam flanking 

 the rivers in low terraces locally known as " second bottoms," 

 while the interfluvial phase is represented by the wide-spread 

 mantle of pine-clad sands stretching scores of miles inland 

 from the coast — though the fluvial phase is sometimes re- 

 moved and the interfluvial phase is more profoundly eroded 

 than in either higher or lower latitudes ; in Georgia the two 

 phases of the formation are similar to those displayed in 

 South Carolina save that both have suffered less from erosion ; 

 in central Alabama the fluvial phase is represented upon the 

 principal rivers by extensive "second bottom" loam (which is, 

 on the Chattahoochee, indistinguishable from the Columbia 

 loam either in hand specimens or in hillsides), while in southern 

 Alabama the loam becomes sandy and expands into a super- 

 ficial mantle of pine-clad sands entering the state from 

 Georgia in a hundred-mile zone which narrows to a twenty- 

 mile belt west of Mobile bay ; in northeastern Mississippi the 

 fluvial deposits are similar to those of northern Alabama, and 

 to the southward they pass into the low-lying sand-plain en- 

 tering the State from the east ; but toward the mouth of the 

 Mississippi the sand-flats narrow, and the sands pass into a 

 series of silts and clays with intercalated sand-beds which are, 

 according to Johnson,* stratigraphically continuous with, and 



*The correlation of the Port Hudson with the Columbia represents the only 

 link in the series which was not established by personally tracing stratigraphic 

 continuity from section to section and from phase to phase on the ground. It is 

 just to say that the coast sands and subjacent clay beds of southeastern Missis- 

 sippi, the Port Hudson, and the loess with its basal gravel bed, were independ- 

 ently and antecedently correlated by Mr. Lawrence C. Johnson of Mississippi, 

 and that the well defined Columbia deposits of the Roanoke river nave been 

 stratigraphically connected with the coast sands and " second bottom " deposits 

 of North Carolina by Prof. Joseph A. Holmes of the University of North Caro- 

 lina, both of whom are engaged in geologic investigations of the Coastal Plain 

 under the auspices of the U. S. Geological Survey and the direction of the au- 

 thor; and it is a source of gratification to be able to state that the observations 

 and inferences of these geologists are in all respects corroborative of the work 

 recorded herein. 



Am. Jour. Sci. — Third Series, Vol. XL, No. 235. — July, 1890. 

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