GEOLOGICAL HISTORY OF THE VIRGINIA COASTAL PLAIX. 211 



During the latter portion of the Paleozoic era the Piedmont floor of the 

 Coastal Plain and also the present Piedmont Plateau seem to have formed 

 a land surface which probably extended far to the east of the present shore- 

 line. How much farther we do not know, but perhaps to the edge of the 

 present continental shelf. The streams draining this land-mass carried 

 great quantities of terrigenous materials to the west where they were 

 deposited in the Paleozoic sea. These strata now form the Blue Eidge and 

 Allegany Plateau of the western portion of the State. During part of the 

 Triassic period a shallow estuary was formed near the eastern margin of the 

 present Piedmont Plateau, into which some of the streams carried their 

 load of sediment, and along the margin of which marsh plants grew in such 

 abundance that their remains now form the coal beds in the vicinity of 

 Eichmond. 



It is of course possible that other changes occurred during the Paleozoic 

 and early Mesozoic periods which have left no record. The region may 

 have been depressed beneath the ocean waters and covered with sediments 

 many times, but if such is the case, later erosion has removed them from that 

 portion of the crystalline surface accessible to our study. Whether sediments 

 of later Paleozoic and early Mesozoic age overlie the older crystallines to the 

 east of the present coast line cannot be with absolute certainty determined 

 but it is within the range of possibility. 



Early Cretaceous history. — The recorded history of the Virginia Coastal 

 Plain begins with early Cretaceous time. The earliest of the known uncon- 

 solidated deposits lying upon the floor of crystalline rocks belong to the 

 Patuxent formation of the Potomac Group. These deposits indicate a sub- 

 mergence of the entire Coastal Plain to perhaps a short distance beyond the 

 "fall line." The water covering the region was shallow and seems to have 

 been estuarine in character. The cross-bedded sands and gravel furnish 

 evidence of the shifting currents as do also the rapid changes in the char- 

 acter of the materials both horizontally and vertically. The presence of 

 numerous land plants in the laminated clays shows the proximity of the 

 land. Since the Patuxent deposits are so very extensive it is somewhat 

 difficult to explain the physical conditions then prevailing. It has been 

 suggested tliat possibly there was a land barrier somewhere to the east, 

 probably beyond the present Atlantic shore-line, which kept out the ocean 

 waters. The presence of large quantities of lignitic material seems to point 

 to the existence of marshes in many places. Continuous deposition did 

 not prevail over the submerged area during the entire time; erosion by 

 means of which some of the earlier Patuxent deposits were destroyed is 



