THE NANJEMOY FORMATION. 201 



species common to the two areas differ widely in their geological range. This 

 is evidently due in part to the difference in physical conditions in the Gulf 

 and middle Atlantic regions and in part, in all probability, to migration. 

 It is apparent, however, that the fauna of the Aquia formation is more 

 closely related to the Wilcox than to earlier or later horizons and that there 

 is a somewhat closer resemblance to the lower than to the upper Wilcox. 



The correlation of the Aquia formation with European deposits is even 

 less definite. Dall correlates'* the entire middle Atlantic coast Eocene with 

 the Suessonian of Europe. It is doubtful, however, whether the Nanjemoy 

 formation should be thus correlated since the writers believe that the Eocene 

 deposits of Virginia and Maryland represent more than the Wilcox of the 

 Gulf and therefore must be regarded as having a wider range in the Euro- 

 pean Eocene. 



The Nanjemoy Formation. 



The Nanjemoy formation has been recognized in Virginia and in south- 

 em Maryland, the materials and fossils being characteristic of the deposits 

 throughout this area. Among the typical forms found in the two states are : 



Corbula aldrichi Meyer Ostrea sellaeformis Conrad 



Meretrix ovata var. ovata (Rogers) Leda improcera (Conrad) 



Meretrix subimpressa Conrad Leda potomacensis Clark and Martin 



Lucina dartoni Clark Nuctila potomacensis Clark and Martin 



Venericardia potapacoensis Clark and 

 Martin 



The ISTanjemoy formation affords species that are characteristic of the 

 upper Wilcox and the lower Claiborne although the relationships are on the 

 whole closer with the former than with the later. It is possible that both 

 may be represented. 



The correlation of the Nanjemoy formation with the European Eocene 

 cannot be satisfactorily made. It is possible that it represents a somewhat 

 higher horizon than the Suessonian and may represent the Londonian and 

 even in part the Parisian. The difficulty in correlating the middle Atlantic 

 Coast Eocene deposits with those of Europe is due to the fact that the few 

 identical species in the two areas have a wide geological range and are thus 

 of little value for purposes of detailed comparison. Other common species 

 may ultimately be -found but more exhaustive collections than have been 

 made will be necessary. Until such investigations are completed the correla- 

 tion of the deposits on the two sides of the Atlantic can be at best only pro- 

 visional. 



al8th Ann. Eept. U. S. Geol. Survey, part 2, pp. 327-348, 1898. 



