22 McGee — Southern Extension of Appomattox Formation. 



At Macon the formation finds typical development. Above 

 the reach of modern alluvium, and above the vaguely defined 

 and poorly exposed " second bottoms " it forms the prevailing 

 surface ; and in every street and suburban road, in every 

 storm-carved runnel and roadside gulley, and in every cutting 

 of the seven railways radiating from the city, its materials are 

 exposed ; and the landscapes are toned by its pure orange, 

 orange-yellow and orange-red tints, or the brick-reds assumed 

 on oxidation. Here the stratification of the deposit is rather 

 less definite and regular than usual, and in some limited expo- 

 sures it is apparently massive. Here, too, the distinctive cross- 

 bedding seen frequently in the south is characteristically dis- 

 played — some beds throughout their entire thickness, and 

 nearly all beds in some part of their thickness or length of 

 exposure, exhibit a rather vague cross-stratification rendered 

 conspicuous under certain conditions of weathering by inter- 

 calated laminae and lines of pellets of white or gray plastic 

 clay. About Macon, too, there is well displayed a character- 

 istic habit of erosion and weathering which is common 

 throughout the south and occasionally seen in the north ; i. e., 

 the exposed and long weathered surface of the deposit takes on 

 a more massive aspect than that of the fresh cutting, the 

 structure lines fade, the rain-cut gullies are transformed into deep 

 and smooth sided amphitheatres separated by broad, even-faced 

 buttresses : the whole forming soft contours. At the same 

 time the exterior portion of the deposit undergoes a slight 

 cementation, and the surface takes on a sort of dull glaze. 

 This peculiarity of weathering is difficult to intelligibly 

 describe, impossible to clearly portray, and yet so character- 

 istic as to be readily recognizable throughout the greater part 

 of the vast field occupied by the formation. About Macon, 

 as in other exposures near the fall-line and on considerable 

 rivers, the formation abounds in small pebbles, arranged in 

 lines, accumulated in pockets, or disseminated throughout the 

 deposit. On the Oconee these pebbles are chiefly of quartz 

 with many of quartzite, and are commonly well rounded or 

 sub-angular ; and it is noteworthy that they are similar in size, 

 material and degree of wear to those found in the subjacent 

 Potomac formation. 



At Macon, as at Columbia, the Appomattox is intercalated 

 between the Columbia and Potomac formations, the Piedmont 

 crystallines being exposed beneath the latter in the vicinity. 

 The Columbia is represented by poorly displayed " second 

 bottoms" and by the sand plains into which the lowlands 

 merge a few miles southeast of the city. These deposits are 

 strongly unconformable to and readily distinguished from the 

 distinctive loams of the Appomattox. The Potomac consists 



