McGee — Southern Extension of Appomattox Formation. 23 



of exceptionally regularly stratified clays and sands, the latter 

 locally containing arkose in considerable quantity, with well 

 rounded pebbles in sheets or pockets and sometimes scattered 

 throughout the mass. It is noteworthy that although the 

 Appomattox and the Potomac are here, as elsewhere, strikingly 

 unconformable, they sometimes merge so completely that no 

 line of demarkation can be drawn with precision. This is fre- 

 quently the case when the Potomac consists predominantly of 

 sand ; when the uppermost stratum consists of clay the 

 contact is usually distinct and sometimes quite conspicuous. In 

 the exposures along the southwestern extension of Fourth 

 avenue the Appomattox and Potomac commonly blend ; in 

 the cutting on the Georgia Central railway at the crossing of 

 Oglethorpe street, the formations are readily distinguishable ; 

 while in the railway cutting four blocks farther southward the 

 contact is distinct in one part of the section, though the 

 deposits appear to merge in another part. 



The finest southern exposures of the three formations so 

 conspicuous and significant in the Middle Atlantic slope are 

 found just below the falls of the Chattahoochee in the villages 

 of Girard and Lively, Alabama, opposite Columbus. As usual 

 there is great unconformity between the "second bottom" 

 loams (by which the Columbia is here represented) and the 

 Appomattox, the latter having been completely removed from 

 a considerable belt flanking the river, while the former rests 

 upon the gneiss and the Potomac arkose throughout a large 

 part of this belt. An analogous relation holds between the 

 Appomattox and the Potomac — an immense volume of the 

 latter having been carried away before the former was laid 

 down. 



The characteristics of the Appomattox in this vicinity are 

 normal, save that the distinctive cross-bed cling outlined in 

 laminae of clay or lines of pellets of the same material is 

 exceptionally conspicuous, that the pebbles are larger, more 

 abundant, and rather less worn than usual, and that there is a 

 notable element of arkose in its composition. In explanation 

 of these slight divergences from the type it should be noted 

 that the Potomac in this locality consists in exceptionally large 

 part of arkose (great beds of it sometimes being scarcely dis- 

 tinguishable from the disintegrated gneiss magnificently dis- 

 played immediately below the lower dam), that certain layers 

 of it consist of exceptionally pure kaolin-like clay, and that 

 its pebbles are larger and less worn than those found upon 

 smaller rivers — or in short, .that the local features of the 

 Potomac are reflected in those of the Appomattox. Contacts 

 between the Appomattox and the Potomac are clearly dis- 

 played in the railway cutting in Lively, and in a natural gulley 



