MAKVf.AM) (ii:()l.()(;if'.\L SURVEY 83 



l'iT(|iiciil ly the same. Il is cNidciil. however, that tlie ^larylaiid lieds 

 c's|H'cially foi'iii the hiwer lidrizoiis. wliile the A'ii'<:iiiia deposits repre- 

 sent iiiort' ]ai\ii'ely the ii|t|ier hoi-i/.oiis of the I'aiiiiiidcey group. In 

 otbiM- words, the Acjiiid t'ni'iiiatioii is iiioic strongly dt'veh)pc'd in ^laryland 

 and the Xanjenioy format ion more str(mgly in Virginia, although the 

 Xanjeiiioy rormatioii is hy no means lacking in Mai'yland and the same 

 is true of the xiquia formation in Virginia. It is apparent that there 

 must have been a gradual transgression of the Eocene deposits south- 

 ward, since the Aquia rormation gradually disappears under the Xanje- 

 moy to the south of' tlio Polomae; on the other hand, the Xanjemoy 

 formation is entirely absent to the northeast of the Patuxent valley, 

 while the Miocene deposits have gradually transgressed over the Eocene 

 from the Potomac valley northward, so that successively older horizons 

 are fonnd in contact with the Miocene in passing from the Potomac 

 basin northeastward toward Delaware, where the Miocene strata ulti- 

 mately come to rest directly on the Cretaceous deposits. The result of 

 this differential movement is to limit the area of outcrop of the Xanjemoy 

 formation in Maryland to the southern counties of the state, Avhile the 

 Aquia formation is continued across the Chesapeake Bay into the eastern 

 counties as well and finally disappears beneath the Miocene cover not 

 far from the borders of Delaware. It is evident, therefore, that higher 

 Eocene horizons are found in central and southern Virginia than appear 

 in Maryland, a conclusion borne out by the fact that the Ostrea sellae- 

 formis zone with its accompanying fossils is much more strongly repre- 

 sented in the valleys of the Pamunkey and James rivers than in the Po- 

 tomac basin. Thick beds of Ostrea seUaeformis are found in the former 

 areas, while only a few representatives of this species appear in the upper 

 zone of the Woodstock substage on the banks of the Potomac. 



COEEELATIOX OF THE DEPOSITS WITH THE EOCEXE FORMATIOXS OF THE 



GULF STATES. 



By common consent the extensive and diversified series of Eocene 

 deposits found in the Gulf region has come to be regarded as the tvpe not 

 only for the Atlantic Coast region but for the entire country as well. 

 Dr. Dall, basing his conclusions both on his own work and on that of 

 others in this area, has recently adopted the following classification of 



