PHYSIOGRAPHIC RECORD 



The history of the development of the topography as it exists to-day is 

 not a complicated one. It has been formed at several different periods 

 during all of which the conditions must have been quite similar. It is 

 merely the history of the development of the four plains already described as 

 occupying different levels and of the present drainage channels. The plains 

 of the Virginia Coastal Plain are all plains of deposition which have been 

 more or less modified by the agencies of erosion. Their formation and sub- 

 sequent elevation to the height at which they are now found indicate merely 

 successive periods of uplift and depression. The drainage channels have 

 throughout most of their courses undergone many changes. Periods of 

 cutting have been followed by periods of filling and the present valleys and 

 basins are the results of these opposing forces. 



Lafayette stage. — Within the borders of the Coastal Plain there is 

 evidence of frequent changes during Mesozoic and early Tertiary time 

 wliich resulted in the deposition of a succession of formations of varying 

 materials. These, however, have been only to a very slight extent influen- 

 tial in producing the present topography. Many of the larger streams 

 evidently occupied their present channels in the Piedmont Plateau during 

 these periods, but their lower courses through the Coastal Plain were 

 obliterated. Even in the early Cretaceous we find that the Coastal Plain 

 deposits formed near the present stream courses consist of much coarser 

 materials that the deposits formed over the divides. In the discussion of 

 the physiographic history of the region as shown by the present topography, 

 the changes which occurred during these periods may be omitted. Towards 

 the close of the Tertiary, however, a change in conditions occurred which 

 is clearly shown in the existing topography. A layer of gravels, sands, and 

 clays was spread over the entire Coastal Plain and on the borders of the 

 Piedmont Plateau during the Lafayette submergence. These deposits must 

 have been laid down on a rather irregular surface, resulting in a com- 

 paratively thin mantle of materials 35 to 30 feet in thickness. When the 

 uplift had terminated Lafayette deposition, a very even, gently sloping plain 

 extending from the Piedmont Plateau to the ocean, bordered the continent. 

 Across this plain composed of coarse and fine unconsolidated materials, 

 streams having their sources in the Piedmont Plateau, gradually extended 

 their courses, while new ones entirely confined to the Coastal Plain were 



