328 ANNUAL REPOET SMITHSONIAN INSTITUTION, 193 3 



Like most other large cities on the Atlantic slope from New Jersey 

 to Alabama, Washington is located at the fall-line, the name given 

 to the junction of the fiat-lying Coastal Plain to the east, composed 

 of sands, clays, and gravels rather recently deposited, and the 

 hilly Piedmont region to the west made up of granites and other 

 ancient hard rocks. It was at the fall-line that the early settlers, 

 pushing their way westward across the Coastal Plain by way of the 

 Susquehanna, Potomac, and other waterways, found their progress 

 impeded by rapids where the hard granites of the Piedmont were 

 encountered. Since these places afforded many natural advantages 

 such as water power, a purer water supply, higher and, therefore, 

 healthier situation, and waterway transportation, they usually 

 marked the beginning of settlements which have since grown into 

 important cities. From north to south these cities — Trenton on the 

 Delaware, Philadelphia on the Schuylkill, Baltimore on the 

 Patapsco, Washington on the Potomac, Richmond on the James, 

 and Augusta on the Savannah — clearly mark the line of contact of 

 the plains and hilly regions. 



Although from the original settlement at Georgetown, Washing- 

 ton might have grown into an industrial city, its selection for the 

 location of the National Capital changed its reason for growth. 



The Atlantic Coastal Plain, including the alluvial valley of the 

 Anacostia River excavated in it, upon which the downtown business 

 section and eastern half of Washington are built, really continues 

 on east beyond the Atlantic seashore resorts and out into the ocean 

 for a distance of 100 miles to the edge of the continental shelf. The 

 sediments which make up the deposits of the entire coastal province 

 have been so recently washed down from the higher lands to the 

 west that the material has not yet had time to consolidate into rock. 

 The process of building up the Coastal Plain still continues. Dur- 

 ing Revolutionary days the American Navy anchored at Bladensburg 

 on the Anacostia River, a side estuary of the Potomac near Wash- 

 ington. Today, however, the water is here scarcely deep enough to 

 reach the hubs of an automobile, and in a few years, unless man 

 intervenes, the area will be dry land. The Coastal Plain has also 

 alternately risen and fallen. Its northern portion has been sub- 

 merged since its first general uplift, so that rivers such as the Po- 

 tomac and Susquehanna, which cross it, were drowned and now 

 occur as wide estuaries, in some instances extending back to the fall 

 line. 



This is the case of the drowned river valley of the Susquehanna 

 known as Cheaspeake Bay, whose beaches offer the geology classes 

 of the Washington schools many geologic phenomena for study. 

 The classic Calvert cliffs, which outcrop for many miles along the 



