330 JfcGee — Formations of the Middle Atlantic Slope. 



upon fossiliferous Miocene beds ; iu the western part of Peters- 

 burg it lies directly upon the Piedmont crystallines ; two miles 

 northeast of Bellfield it cannot be clearly demarked from the 

 fossiliferous Miocene; and at Wei don it rests upon deeply ra- 

 vined crystalline rocks save where inconspicuous remnants of 

 Potomac arkose intervene. It therefore reposes upon a founda- 

 tion made up alike of Piedmont crystallines, Potomac deposits, 

 Eocene clays and greensands, and Miocene beds, all of which, 

 with the possible exception of the last, were deeply degraded 

 before its deposition. 



The formation is overlain only by the alluvium of small 

 streams, aeolian sands, etc., on the broad plains between Peters- 

 burg and Weldon, by occasional accumulations of wave-washed 

 debris derived from its own mass in the extensive Quaternary 

 terraces prevailing in its area, and by the characteristic clays, 

 sands, and gravels of the Columbia formation in the vicinity of 

 the larger streams. 



Taxonomy.-— Since the formation has yielded no fossils, its 

 age and relations can only be determined by stratigraphy, de- 

 gree of alteration of materials, depth of erosion, etc. It is mani- 

 festly newer than the fossiliferous Miocene upon which it rests, 

 and older than the Columbia formation by which it is overlain; 

 and its fresh aspect and comparatively slight erosion indicate 

 that its place is much nearer the later than the earlier of these 

 formations. 



The Appomattox formation is stratigraphically continuous 

 with an extensive series of clays and sands investigated in 

 North Carolina by Kerr, and referred by him first to the Quater- 

 nary and subsequently to the Eocene. Since the role played by 

 these deposits is increasingly important southward, and since 

 they have been casually recognized at many points in the 

 Southern Atlantic slope, it is probable that they will be found 

 to reach considerable volume in South Carolina, Georgia, and 

 Alabama; and although precise relations have not yet been 

 ascertained, it is indicated not only by physical considerations 

 but by Fontaine's recent studies in Virginia and Alabama that 

 at least a part of the Orange Sand of Hilgard and other 

 southern geologists is equivalent to the Appomattox formation 

 of the north rather than the Columbia, which is not known to 

 extend much farther southward than North Carolina. (It 

 should be noted that a part of the deposits designated " Orange 

 Sand " by different geologists consist of re-arranged residuary 

 debris of the Tuscaloosa and perhaps other formations.) 



Too little is yet known of the Appomattox formation to 

 warrant minute interpretation of its history or correlation of 

 its record either with those of other deposits of the Atlantic 

 ■ Slope or with the degradation records of the Piedmont and 

 Appalachian hills. 



[To be continued.] 



