CENOZOIC. 89 



homogeneous. There is seUlom any difficulty experienced in drawing the 

 line of separation between the Eocene strata and the overlying and under- 

 lying formations. The great amount of glauconite in the Eocene deposits 

 and the homogeneity of the deposits as a whole, at once separate them from 

 the extremely variable and highly colored sands and clays of the Potomac 

 formations below, and from the blue clays, light colored sands, and diato- 

 maeeous earth beds of the overlying Miocene. 



Even though the Eocene deposits have characters so persistent that they 

 can readily be separated from adjacent formations, yet recent investigations 

 have shown the possibility of dividing the deposits into two well-marked 

 formations on both lithologic and faunal grounds. These formations have 

 received the names of Aquia and Nanjemoy. The Eocene deposits of Mary- 

 land and Virginia were first supposed to constitute a single stratigraphic 

 unit which was called the Pamunkey formation. Since the division of the 

 deposits into two formations the term Pamunkey is retained as a group 

 name. The lower or Aquia formation is much more highly arenaceous than 

 the upper or Nanjemoy formation which, particularly in its lower part, is 

 generally highly argillaceous. The Aquia formation is also much more 

 calcareous than the JSTanjemoy formation, indurated layers frequently appear- 

 ing in the former. Both formations are, however, highly glauconitic. 



The most complete section of the Eocene strata in the Middle Atlantic 

 Slope is afforded by the series of high bluffs on the western bank of the 

 Potomac Eiver between Aquia Creek and Mathias Point, in eastern Staf- 

 ford and King George counties. The peninsula between the Potomac and 

 Eappahannock rivers is to a large extent formed of the Eocene greensands, 

 which also appear along the banks of the latter stream, outcropping beneath 

 the Columbia formations. The higher levels of the intervening country 

 are, however, generally capped by the Miocene and Columbia formations. 



The Eocene deposits are continued southward in Spottsylvania. and 

 Caroline counties. Fine bluffs of the characteristic marls appear on the 

 south bank of the Rappahannock at several points above Port Eoyal, but in 

 the vallev of the ]\Iattaponi they are mucli less prominent although oc- 

 curring at frequent intervals. An extensive cover of later deposits occupies 

 the higher portions of the country. In the valley of the Pamunkey River 

 and its tributaries, particularly in Hanover County, important outcrops of 

 Eocene strata are found. For this reason the name Pamunkey was first 

 selected as the name for the formation. Many of the fossils described by 

 Conrad and Rogers were obtained along the Pamunkey River. 



Farther south, in the valley of the James River, there are many excellent 

 outcrops of Eocene material exposed at intervals from Richmond to a short 



