24 McGee — Southern Extension of Appomattox Formation. 



half a mile northwest of this point; in the former exposure the 

 formations are distinct throughout the greater part of the 

 exposure, but inseparable with any degree of accuracy in 

 another part ; while in the second exposure the regularly 

 bedded orange-brown loams of the Appomattox, with a pebble 

 bed at the base, are conspicuously demarked from the creamy- 

 white, cross-stratified arkose of the Potomac. The best expo- 

 sures of the Appomattox occur in the scarp of a fairly well 

 defined terrace about a hundred feet above the low-water level 

 of the river (below the falls) in the village of Girard. 



Eminently satisfactory exposures of the Appomattox occur 

 about Montgomery (particularly in cuttings on the M. & E. 

 railway in the southeastern part of the city), where it rests 

 unconformably upon the Eutaw sands, the junction being 

 sometimes marked by a ferruginous crust, again by a sheet of 

 pebbles, and elsewhere by a decided difference in hue, though 

 it is sometimes indistinct ; but the characters of the formation 

 here are in no way specially noteworthy save that the pebbles 

 contain an exceptionally large element of quartzite or semi- 

 quartzitic sandstone, together with large numbers of subangular 

 fragments of chert and siliceous dolomite. 



The numerous excellent exposures of the formation about 

 Tuscaloosa are noteworthy in that they form a definite terrace, 

 evidently of considerable antiquity though probably restored 

 in part during the Columbia epoch, upon which the city as 

 well as the State University and Insane Hospital are located. 

 They are also noteworthy in that the pebbles comprise cherts, 

 siliceous dolomites, and a rather unimportant element of 

 quartzite, but no true crystallines. The pebbles are notably 

 smaller and less worn than in the more easterly and northerly 

 localities. Here as elsewhere about the fall-line the formation 

 is overlain unconformably by the Columbia, and in turn overlies 

 with still greater unconformity the Potomac — the Tuscaloosa 

 formation of Smith and Johnson ; yet here as in other locali- 

 ties these formations of widely diverse age sometimes merge 

 so completely that no sharp line of demarcation may be drawn 

 between them. This is notably the case in the railway cutting 

 at Cottondale, seven miles east of Tuscaloosa, where the Poto- 

 mac is a cross-stratified gravel with a matrix of sand, and the 

 Appomattox a horizontally bedded mass of similar gravel in a 

 matrix of loam ; yet usually despite this discordant bedding, 

 the materials merge. In some of the cuttings on the A. G. S. 

 railway between Cottondale and Tuscaloosa, however, the 

 junction is marked either by ferruginous crusts or by sheets of 

 pebbles of ferruginous sandstone evidently derived from the 

 older formation. 



Earther southward the formation is displayed at several 



