20 IfcGee — Southern Extension of Appomattox Formation. 



in various exposures in this region; both resemble in some 

 measure characteristic aspects of the Potomac formation seen 

 in eastern Virginia ; and it is significant that the Potomac is 

 not found here (probably by reason of removal through degra- 

 dation), that crystalline rocks approach and in the immediate 

 vicinity reach the surface, and so that the Appomattox probably 

 rests immediately upon the eastward extension of the ancient 

 Piedmont crystallines. 



Nearer the coast the formation is frequently exposed in rail- 

 way cuttings and displays the features characteristic of the 

 contemporaneous deposits north of the Roanoke, save that the 

 orange tints are less pronounced and mixed with browns and 

 grays in some strata, that the bedding is thinner and more 

 pronounced, and that pebbles are small and rare. It is signifi- 

 cant that the aspect of the formation here approaches that dis- 

 played by the phosphate-bearing Pliocene beds of the South 

 Carolina coast. 



Another distinctive but hardly distinct aspect of the forma- 

 tion is extensively displayed in central South Carolina, notably 

 about Columbia. Here the usual moderately regular and 

 rather heavy but always inconspicuous bedding of the forma- 

 tion is displayed ; but the prevailing colors are richer and 

 darker than in other parts of the terrane, commonly ranging 

 from orange red to chocolate brown. Moreover certain of the 

 strata exhibit a peculiar mottling (which is better displayed 

 farther southward) ; certain other strata exhibit a distinctive 

 cross stratification defined by gray or white plastic clay in laminse, 

 irregular sheets, and lines of pellets ; the various strata are 

 more uniform in composition than in the north, consisting 

 rather of loam than of sand and clay in alternating beds ; and 

 the deposit as a whole takes on a solid, massive, and rock-like 

 appearance, and gives origin to a distinctive topography. So 

 conspicuously diverse in color, texture, and habit of erosion are 

 the prevailing formations of central South Carolina that over 

 thousands of square miles the surface is popularly divided into 

 "red hills" and "sand hills" — the former representing the 

 Appomattox, and the latter the southern interfluvial phase of 

 the Columbia formation. The distribution of pebbles in this 

 vicinity is especially interesting: Northeast of the Congaree 

 river on the line of the Richmond and Danville railway, peb- 

 bles are rare to within two miles of the present waterway; 

 there they suddenly increase in abundance, and in some sections 

 within a mile from the river form a considerable and some- 

 times the principal part of the deposit ; while south of the 

 river they quickly become rare, being abundant only within 

 a mile or less of the river bluffs. The pebbles are predomi- 

 nantly of quartz though partly of quartzite, and comprise a 



