the Middle Atlantic Slope. 123 



rock margin for scores of miles before finally finding their way 

 into the open ocean. By this deflection of the rivers the north- 

 ern half of the Coastal plain is nearly insulated ; the isthmuses 

 between the Raritan and the Delaware, between Claybank 

 creek and Elk river, between the Patapsco and the Anacostia, 

 and between Potomac creek and the Rappahannock, from tide- 

 water to tide-water, are low, and but 20, 15, 25, and 5 miles 

 in width respectively ; measured directly along the fall-line, so 

 that, the Hudson is barred from the Rappahannock by only 

 about 60 miles of land and unnavigable water. The deflected 

 portions of the rivers indeed occupy a great trough skirting and 

 accentuating the Piedmont escarpment.* This remarkable 

 physiography has materially affected the culture of the region : 

 The pioneer settlers of the country ascended the tidal canals to 

 the falls of the- rivers where they found, sometimes within a 

 mile, clear fresh water, the game of the hills and woodlands 

 and the fish and fowl of the estuaries, and, as the population in- 

 creased, abundant water-power and excellent mill sites, easy 

 ferriage and practicable bridge sites ; here the pioneer settle- 

 ments and towns were located ; and across the necks of the in- 

 ter-estuarine peninsulas the pioneer routes of travel were ex- 

 tended from settlement to settlement until the entire Atlantic 

 Slope was traversed by a grand social and commercial artery 

 stretching from New England to the Gulf States. As the 

 population grew and spread, the settlements, villages, and towns 

 along this line of Nature's selection waxed, and many of them 

 yet retain their early prestige — for Trenton, Philadelphia, 

 Wilmington, Baltimore, Washington, Fredericksburg, Rich- 

 mond, and Petersburg are among the survivors of the pioneer 

 settlements; and the early stage route has become a great 

 railway and telegraph line connecting North and South as they 

 were connected of old in a more primitive fashion. The in- 

 fluence of natural conditions upon man and his institutions is 

 nowhere else more strikingly exemplified. 



No discussion of the phenomena of the Atlantic slope is 

 intelligible without clear comprehension of the great physio- 

 graphic divisions into which it is naturally separated. These 

 divisions are represented graphically in the accompanying 

 stereogram, which also exhibits the essential continuity of the 

 Coastal plain to the great submarine escarpment off the Atlan- 

 tic coast ; the submarine profiles being based on soundings by 

 the Coast Survey, the Fish Commission, etc., while the indi- 

 cated sub-marine structure is hypothetic. 



* It is shown elsewhere (7th Annual Report, TJ. S. Geol. Survey) that this 

 trough is due to a post-Tertiary displacement aloDg which movement is now in 

 progress, probably at a rate as high as in the well-known recent faults of the 

 Wasalch or the Sierras. 



