116 THE GEOLOGY OF PRIXCE GEORGe's C0U>;TV 



The Pleistocene Formations, 

 the columbia group. 



The Pleistocene fonnations of the .Vthmtic Coastal Plain are 

 united under the name Columbia group. They have many charac- 

 teristics in common, owing to their similar origin. They consist ot 

 gravel, sands, and loam which are stratigraphically younger than the 

 Lafayette formation. The Columbia group in this area comprises 

 three formations, the Sunderland, Wicomico, and Talbot. They ap- 

 pear as the facings of different plains or terraces, possessing very 

 definite physiographic relations (see fig. 2), as described under the 

 heading ''Topographic features." 



On purely lithologic grounds it is impossible to separate the three 

 formations composing the Columbia group. The materials of all 

 have been derived mainly from the older formations which occur in 

 the immediate vicinity, but include more or less foreign material 

 brought in by streams from the Piedmont Plateau or from the 

 Appalachian region beyond. The deposits of each of these forma- 

 tions are extremely varied, their general character changing with 

 that of the underlying formations. Thus deposits belonging to the 

 same formation may, in different regions, differ far more litholog- 

 ically than deposits of two different formations lying in prox- 

 imity to each other and to the common source of most of their 

 material. Cartographic distinctions based on lithologic differences 

 could not fail to result in hopeless confusion. At some places the 

 older Pleistocene deposits are more indurated and their pebbles more 

 decomposed than those of the younger formations, but these differ- 

 ences can not be used as criteria for separating the formations, inas- 

 much as loose and indurated, fresh and decomposed materials occur 

 in each of them. 



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

 much service in separating the deposits into distinct formations, even 

 though essential differences between some of them may exist. It is 

 the exceptional and not the normal development of the formations 

 that has rendered the preservation of fossils possible. These consist 

 principally of fossil plants that were preserved in bogs, but in a fe'.v 



