CORRELATION OP DEPOSITS. 



353 



criteria for correlation are more complete. The physical characteristics 

 and organic remains of the Potomac formation of the Atlantic border 

 have generally led to its correlation with the Tuscaloosa of the eastern 

 Gulf, which occupies a similar position at the base of the Coastal Plain 

 series. These basal deposits are generally regarded to be of Lower Cre- 

 taceous age and to be the sole representatives of it east of the Mississippi 

 river. 



It is highly probable that the more distinctly marine beds of the up- 

 per Cretaceous rest throughout this portion of the continental border 

 unconformably upon the older deposits, but whether their basal strata 

 are synchronous everywhere has not as yet been definitely proven. 

 Enough has been learned, however, from a comparison of the species of 

 the Matawan-Monmouth groups with the Eutaw-Rotten Limestone- Ripley 

 groups to show that they have a common fauna. This is very clear as 

 regards the Ripley and Rotten Limestone groups, while there is nothing 

 in the meager assemblage of forms from the Eutaw group to debar it 

 from being included also. Stanton has found that these Upper Creta- 

 ceous deposits in Mississippi have 86 species in common with the New 

 Jersey strata, while in Alabama 35 have been found, all of which are 

 also included in the list from Mississippi. At the same time 54 continue 

 on into Texas. It is highly probable, then, that the Matawan-Monmouth 

 formations stand as the representative of the upper Cretaceous of the 

 eastern Gulf region. 



Before considering the succeeding groups of formations (Rancocas- 

 Manasquan-Shark River), all of which contain faunas of post-Ripley age, 

 let us examine the typical Eocene fauna of the Pamunkey formation of 

 Delaware, Maryland, and Virginia, which is the next succeeding member 

 of the Coastal Plain series. A critical examination of the fossils from 

 this formation shows two quite distinct faunal zones. The lower, about 

 60 feet from the bottom of the formation in the Potomac vallev, has been 

 designated the Aquia Creek fauna, and shows many points of similarity 

 to the middle Lignitic of the Gulf, while the upper or Woodstock fauna, 

 containing Ostrea sellteformis and other types, finds its approximate 

 equivalent in the Claiborne, or rather that zone represented below the 

 fossiliferous sands. With proper allowance for differences in physical 

 .conditions and the consequent effect upon geological range of species, for 

 time occupied in migration, and for the lack of typical forms in the high- 

 est and lowest strata, the Pamunkey may be regarded as the equivalent 

 of all or the major part of the Lignitic, Burhstone, and Claiborne of the 

 Gulf, although no assumption is made that deposition began at just the 

 same time in the one region as in the other. Some portions of the basal 



