30 IfcGee — South* rn ExU tision of Appomattox Formation. 



commonly known as Bnhrstone — the Choctaw buhrstone of 

 Smith ; its rocks are the most obdurate of the entire Neozoic 

 series within the Gulf slope, and so its general surface is ele- 

 vated and sculptured into a complex configuration of pro- 

 nounced relief and sharp contours ; yet despite these conditions 

 so exceptionally favorable to degradation, the Appomattox 

 frequently maintains its integrity over considerable areas. 

 Beyond the hill-land of the buhrstone lies the lowland formed 

 by the predominantly calcareous newer Eocene formations — 

 the Claiborne, Jackson and Yicksburg — over which the Appo- 

 mattox is again trenched by almost every waterway and 

 reduced to ragged remnants only more extensive than those 

 overlying the Tombigbee chalk ; but upon the silico-argilla- 

 ceous terrane of the Grand Gulf the remnants once more 

 expand until they form the greater part of the surface, save 

 along the larger waterways, as about Hattiesburg in Central 

 Mississippi. In short, the formation is generally preserved 

 over loamy and clayey terranes, much more seriously invaded 

 by erosion over sandy terranes, and largely degraded over 

 calcareous terranes ; and this is true not only of the section 

 from Tuscaloosa to Hattiesburg in Alabama and Mississippi, 

 but of the formation as a whole. 



It has already been intimated that the composition of the 

 Appomattox everywhere depends in part upon that of the sub- 

 terrane, i. e., that its materials everywhere consist of local 

 elements and erratic elements combined in varying propor- 

 tions ; and the variable friability and solubility resulting from 

 this inequality in composition is evidently the reason for the 

 unequal resistance which the formation has offered to degrada- 

 tion in various parts of its extent. 



Htpsographic Distribution. 



The best development of the formation in Virginia and 

 North Carolina lies between 25 and 150 feet, and its upper 

 limit is probably less than 250 feet, above tide. Farther 

 southward the lower observed limit remains about the same, 

 while the upper rises to at least 650 feet over the divide 

 between the Congaree and Savannah, where the formation is 

 well developed and constitutes the prevailing surface. The 

 lowest altitudes at which it has been observed near the Gulf 

 are less than 25 feet above tide at Nicholson and not much 

 higher at Grand Bay ; and the greater altitudes in the Gulf 

 slope are not less than 450 feet in uplands near Tuscaloosa, 

 and 600 feet in the Buhrstone hill-lands west of Meridian.* 



* It has recently been found washed by tide waters on the east side of Mobile 

 bay, by Mr. L. C. Johnson. 



