the Middle Atlantic Slope. 381 



South of the Potomac river the deposits and terraces remain 

 conspicuous,though their maximum altitudes diminish: Occoquan 

 river, Acquia creek, and neighboring streams have well-marked 

 terrace-systems built of deposits of uniform structure, though 

 each deposit is made up of the materials traversed by the 

 individual stream ; the Rappahannock valley is fashioned into 

 terraces miles in extent and flanked by brick clays passing into 

 gravel and bowlder beds made up of the Piedmont rocks and 

 well-rounded gravel derived from the adjacent Potomac beds, 

 the whole resembling the delta of the. Potomac river so closely 

 that a typical section in one would equally represent the 

 other; the Taponi and the Mat have corresponding deltas 

 which unite and flank the Mattaponi for miles, and the two 

 Anna rivers exhibit similar deposits of greater volume merging 

 along the Pamunkey ; the superficial deposits about the head 

 of tide in James river are so similar to those of the Potomac 

 that Plates YI and YII could be almost exactly duplicated 

 there, though the area of the delta is somewhat greater and its 

 altitude somewhat less than that of the latter river ; the Ap- 

 pomattox has its elevated delta which merges into that of the 

 James, but is distinguished in the vicinity of Petersburg by 

 an independent system of terraces and by the preponderance 

 of local rocks ; the Nottoway and Meherrin also exhibit well- 

 developed deposits of the usual bipartite structure, as do the 

 smaller streams, Rowanty, Stony, and Fontaine ; and finally 

 the Roanoke embouches from its narrow Piedmont gorge into 

 a tidal estuary flanked by low bluffs built of or capped by the 

 prevalent brick clay and gravel with local bowlders. 



The maximum altitude of the deposits, which is 5.00 feet on the 

 Susquehanna and 400 feet or more on the Delaware, diminishes 

 southward to perhaps 275 on the Schuylkill, 245 at the mouth 

 of the Susquehanna, 145 feet (with inconspicuous deposits 

 somewhat higher) on the Potomac, 125 feet on the Rappahan- 

 nock, 100 feet on the James, and 75 feet on the Roanoke ; and 

 as already pointed out,* the maximum size of the bowlders in 

 the lower member, as compared with those now transported by 

 the rivers, diminishes from 50:1 on the Susquehanna to 20:1 on 

 the Potomac, 10:1 on the Rappahannock. 5:1 on the James, and 

 2 or 3 times the present volume on the Roanoke. 



Recapitulation. — Briefly, the deposits along the Middle At- 

 lantic slope rivers about their loci of transition from fluvial 

 to estuarine condition are so closely similar that not only will 

 the description of a typical section on one waterway apply to 

 those of all the others, but it would in most cases be difficult 

 to determine from the most minute examination which stream 



*This Journal, III, xxxiv, 219, 1887. 



