328 W. J. McGee — Three Formations of 



Art. XXYII. — Three Formations of the Middle Atlantic 

 Slope ; by W. J. McGee. 



(Continued from page 143.) 

 The Appomattox Formation. 



Character and Distribution. — Near the summits of the bluffs 

 overlooking the Rappahannock river from the southward a mile 

 or two west of Fredericksburg, a distinctive, stratified, orange- 

 colored sandy clay is found reposing upon Potomac sandstone, 

 from which it is readily distinguishable by its greater homo- 

 geneity, the more complete intermingling of its arenaceous and 

 argillaceous materials, its more regular stratification, and its 

 more uniform and predominantly orange color. It is as readily 

 distinguishable from the Columbia deposits, on the other hand, 

 by its vertical homogeneity, its comparatively regular stratifica- 

 tion, its distinctive color, and its greater range of altitude — 

 extending as it does from tide-level to the highest eminences of 

 the Piedmont escarpment between the Rappahannock and the 

 Roanoke. At Fredericksburg the deposit is commonly thin 

 and confined to limited isolated areas, especially at the higher 

 levels, and it appears at but a single locality (Potomac creek) 

 north of the immediate valley of the Rappahannock ; but it 

 rapidly increases in thickness and continuity to the southward. 

 About the confluence of the JSTi, Po, and Ta rivers it forms the 

 surface over a meridional zone fully 10 miles wide ; it is well 

 exposed in the bluffs of the Taponi, along which it reposes upon 

 the f ossiliferous Eocene ; and in the bluffs of the Mattaponi and 

 the Anna rivers, as well as over the intervening divides, it is the 

 prevalent surface formation, maintaining the characteristics ex- 

 hibited at Fredericksburg save that it is frequently gravelly. In 

 the vicinity of Richmond it is occasionally exposed toward the 

 summits of the river bluffs, but is there less conspicuous than 

 the subjacent Miocene, Eocene and Potomac deposits ; while 

 still further southward it continues to thicken and expand. 



The distinctive orange-colored sands and clays of the forma- 

 tion are typically exposed on and near the Appomattox river 

 from its mouth to some miles west of Petersburg. A mile 

 below Petersburg they are found at tide-level in the river banks ; 

 in the eastern part of the city they appear overlying the f ossil- 

 iferous Miocene beds mid-height of the bluffs ; and at the 

 " Crater " a mile and a half east, in the railway cuttings in the 

 southwestern part, and on the upland two miles west of the 

 city, they occupy the highest eminences. The zone of out- 

 crop here is at least 30 or 40 miles wide. As at Fredericks- 

 hurg, the deposit is a regularly but obscurely stratified orange- 



