GEOLOGICAL HISTORY OF THE VIRGINIA 

 COASTAL PLAIN 



The formations which occur within the Virginia Coastal Plain are in 

 every case continued either to the north or to the south and the geo- 

 logic history which is here outlined has been based on work done not only 

 in the Virginia area but also throughout the entire region of the North 

 Atlantic Coastal Plain from New England to the Carolinas. 



A study of the geologic history of the region shows that it has been a 

 long and complicated one. This is evidenced by the many different kinds 

 of strata represented and by the relations which they bear to one another. 

 There are deposits that were plainly formed in fresh or brackish water, 

 while others show evidence of deposition in marine waters; some have been 

 deposited in water of shallow depth, others in deeper water; while breaks 

 in the continuity of the different strata indicate that the region has 

 been subjected to many elevations and subsidences from the time of the for- 

 mation of its earliest rocks down to the present day. 



Pre-Cretaceous history. — The oldest Coastal Plain deposits are of Lower 

 Cretaceous age. They can be found everywhere resting upon crystalline 

 rocks of probably pre-Cambrian and early Paleozoic age. These form the 

 floor upon which the Coastal Plain deposits have been laid down, a floor 

 which near the present shore-line lies about 2,000 feet beneath the sea level, 

 but which rises to the west and finally appears at tlie surface to form the 

 Piedmont Plateau, the physiographic province which forms the western 

 boundary of the Coastal Plain. 



In the Piedmont it is exceedingly difficult to interpret the past history 

 for the reason that the whole area has been subjected to many great changes 

 which have essentially modified original materials, yet the studies that have 

 been carried on have revealed many facts concerning the original conditions 

 of the rocks now composing it. Many of these were originally sedimentary 

 deposits, but in the processes of metamorphism have now lost nearly all 

 traces of their original character. Furthermore these old sedimentaries 

 have been broken through in many different places by igneous materials 

 which have also been greatly altered. Thus the Piedmont metamorphics 

 contain representatives of both igneous and sedimentary rocks. Time and 

 again they have been subjected to the various processes of metamorphism by 

 which the original mineral composition has been greatly changed, and the 

 beds have been folded and crumpled. 



