QUATERNARY. 179 



QUATERNARY. 



The Quaternary deposits of the Virginia Coastal Plain belong to the 

 Pleistocene and Recent epochs, both well represented by surface deposits 

 which although thin have a very wide areal distribution. Together they 

 conceal almost all of the older formations except along the valleys where 

 stream cutting has ex})osed them.. 



PLEISTOCENE. 



COLUMBIA GROUP. 



The Pleistocene formations of the Atlantic Coastal Plain are united 

 under tlie name of Columbia group. The name Columbia was first 

 employed as a formation name, when it was believed that the Pleistocene 

 deposits of the region represented a single stratigraphic unit. Later a two- 

 fold classification of the Pleistocene was recognized and the formations were 

 designated as the Earlier and Later Columbia. Further investigation 

 revealed the fact that the Later Columbia deposits should also be divided. 

 The formations have been given the names of Sunderland, which is the 

 equivalent of the Earlier Columbia, and Wicomico and Talbot wliich con- 

 stitute the Later Columbia. 



The Columbia deposits consist in general of gravel, sand, and loam. On 

 purely lithologic grounds it is impossible to separate the three formations. 

 In each case the deposits have been derived mainly from the older forma- 

 tions which occur in the imnu'diate vicinity with which is mixed more or less 

 foreign material brouglit in by streams from the Piedmont Plateau or from 

 the Appalachian region beyond. The deposits of each of these formations are 

 extremely variable and change character according to the underlying forma- 

 tions. Thus materials belonging to the same formation in adjacent regions 

 may differ far more lithologically than the materials of two different forma- 

 tions, lying in proximity to each other. At times the older Pleistocene 

 deposits are somewhat more indurated and the pebbles more decomposed than 

 in the case of the younger formations, l)ut these differences have small 

 value as criteria for the discrimination of the formations, since loose and 

 indurated and fresh decomposed materials occur in each of the formations. 



The fossils found in the Pleistocene deposits are far too meager to be of 

 n)uch service in differentiating the formations. It is the exceptional and 

 not the normal development of the formations which has rendered the pre- 

 servation of fossils i^ossible. They consist principally of plants preserved 

 in fossil bogs, although in a few widely separated places deposits contain- 

 ing great numbers of nuirine and estuarine molluscs have been found. 



