34 McGee — Southern Extension of Appomattox Formation: 



not only the Appomattox but also the basal gravel beds of the 

 Pleistocene loess, parts at least of the Cretaceous or Jurassic 

 Potomac (Tuscaloosa) formation, and other deposits of various 

 ages, none of the old designations can be retained without 

 material modification in definition. It therefore seems wise 

 to extend the term applied to the formation in the region in 

 which it was first studied and clearly defined. 



Sourcks of Materials. 



The materials of the formation which may be certainly traced 

 to their sources are (1) pebbles or gravel, (2) arkose, and (3) a 

 certain portion of the more finely divided matter. 



It has been stated incidentally that about the fall-line the 

 pebbles of the Appomattox are in large part identical with 

 those of the Potomac, and that they are evidently derived 

 therefrom. It has also been stated incidentally that the pebbles 

 of both Appomattox and Potomac vary from river to river 

 — quartz on the Rappahannock, quartzite with less quartz on the 

 James and Appomattox, quartz with less quartzite on the 

 Roanoke, quartz mainly on the Neuse and Cape Fear, quartz 

 with less quartzite on the Santee system, quartz and quartzite 

 in nearly equal proportions on the Savannah and Ocmulgee, 

 quartzite with less quartz on the Chattahoochee, quartzite, silic- 

 eous dolomite, quartz, and chert (in order of abundance) on the 

 Alabama, siliceous dolomite, chert, and quartzite on the Tusca- 

 loosa (or Warrior), and chert on the Pascagoula and Pearl ; 

 and this variation goes exactly with the petrographic char- 

 acter of the most obdurate rocks traversed by the upper reaches 

 of the respective rivers. 



Arkose is but a limited and unusual constituent of the 

 formation, and is only known to occur under two sets of con- 

 ditions: It occurs when the formation rests directly upon 

 crystalline rocks or when these rocks are exposed in such 

 proximity as to indicate absence of deposits intermediate in 

 age, as at Wilson, N. C. It occurs also, in less abundance and 

 purity, where the Appomattox rests directly upon the Potomac 

 formation and the latter is made up largely or exclusively of 

 the same material, as at Girard, Alabama. In both cases the 

 material is evidently derived from an adjacent and older forma- 

 tion. 



Certain striking features in geographic distribution of the 

 Appomattox formation already pointed out indicate that in 

 many if not in all cases a part of its materials were derived 

 from immediately subjacent strata, and so that the character of 

 this formation in a measure reflects that of the sub-terrane — 

 the characteristic orange loams being exceptionally loamy over 



