16 JlcGee — Southern Extension of Appomattox Formation. 



the globe. Yet in the south as in the north the boundary is 

 the most important structural line of eastern United States : 

 it marks the junction of the unconsolidated and practically 

 undisturbed Neozoic elastics on the seaward side, at first with 

 the greatly disturbed crystallines, and then with the corru- 

 gated, folded, and everywhere completely lithified Paleozoic 

 strata of the southern Appalachians ; on reaching it every 

 stream, great and small, is broken by a rocky rapid, a great 

 fall, or a cascade, and these lines of rapids, falls, and cascades 

 extend from the Roanoke almost to the Mississippi. And in 

 the Southern Atlantic and Eastern Gulf slopes, as in the 

 Middle Atlantic zone, the boundary is an important cultural 

 line : Most of the leading southern cities are built at the falls 

 of the rivers, and their industries are determined by the water- 

 power which the rivers afford ; the rivers are commonly 

 navigable below and unnavigable above the falls, and the 

 original means of traffic were thus diverse, and this diversity 

 persists in some measure to-day ; while the soils on opposite 

 sides of the boundary are essentially distinct, and so the in- 

 dustries growing out of the soil and its products are commonly 

 sharply contrasted. Among the southern cities located 

 on the fall-line are Columbia, Augusta, Macon, Columbus, 

 Montgomery and Tuscaloosa. The Coastal Plain lying between 

 this great structural, physiographic, and cultural boundary of 

 Nature's drawing and the still more trenchant boundary 

 marked by the shores of the Atlantic and Gulf, is a lowland 

 zone, concentric with the continent save as expanded by the 

 Floridian peninsula, and scored radially by drainage lines, of 

 which many expose its structure. 



This is the area in which the Appomattox formation is 

 found ; and throughout the greater part of this area, the 

 formation is well developed and wonderfully presistent in 

 composition, structure, and stratigraphic relations. 



In order to set forth clearly the phenomena of the Appo- 

 mattox formation in its southern extension, it is necessary to 

 note briefly the characteristics in the southern states of the 

 two great data-formations representing the beginning and the 

 ending of Neozoic time in the Middle Atlantic slope — the 

 Potomac and the Columbia. 



About its type locality (the District of Columbia), the 

 Columbia formation exhibits two phases, i. e., a fiwuial phase, 

 consisting of brick-clay or loam graduating downward into a 

 gravel or bowlder bed; and an interfluvial phase, consisting 

 largely of debris derived from the immediately subjacent 

 formations, rearranged, intermixed with a variable element of 

 far traveled material brought down by the rivers, and re- 



