52 PHYSIOGRAPHY AXD GEOLOGY OF THE COASTAL PLAIN PROVIXCE. 



SAND DUNES. 



In various places both on the eastern and western shores of the Chesa- 

 peake Bay there are accumulations of wind-blown sand of recent origin. 

 These are most abundant where the surface soils are composed of loose fine 

 sand but they also occur along the ocean border where they have been 

 built up from beach sand. Most of these sand dunes are low banks of sand, 

 seldom more than 10 feet in height and arranged in long windrows at right 

 angles to the usual trend of wind movement. In general the lee side of a 

 sand dune is steeper than the windward side. Many observations of the 

 low dunes on the Eastern Shore show them to have a general northeast and 

 southwest direction, those some miles from the ocean front having the 

 steeper side to the southeast, indicating that the northwest winds of winter 

 the much more influential in their formation than are the prevailing south- 

 westerly winds of the summer season. 



The largest dunes of the Virginia Coastal Plain are the beach dunes 

 along the ocean and bay shores in the vicinity of Cape Henry. These 

 parallel the shore for a distance of several miles and are composed of the 

 beach sand blown inward by landward-moving winds. The dunes at Cape 

 Henry reach an elevation of 70 feet. The ocean slopes are very gentle while 

 the landward slopes are steep. These dunes are advancing landward and are 

 now encroaching upon a forest, some of the trees of which have already been 

 buried. The movement, however, is a very slow one as the present condition 

 of the dunes is not very different than when described by B. H. Latrolie" 

 in 1799. 



DRAINAGE. 



An almost complete surface drainage system has been developed in the 

 Virginia Coastal Plain although the topography is comparatively recent. 

 There are a few natural fresh-water lakes or ponds while fresh- water marshes 

 are almost entirely confined to the borders of the sluggish streams. Tlie 

 Dismal Swamp and Lake Drummond are the notable exceptions, yet they 

 are not the only ones, for in some places there occur over the higher-lying 

 divides small undrained areas in which the surface water collects during 

 the rainy season to form small ponds or SAvamps which are desiccated during 

 the summer months. Usually, however, the surface soil and subsoil are so 

 porous that underground drainage is effected when the surface drainage 

 system is incomplete. It is thus that considerable areas to the southeast 

 of Norfolk are drained. 



oTrans. Amer. Philos. Soc. 1700, Vol. iv. pp. 430-444. 



