CENOZOIC HISTORY. 579 



overwash deposits, or talus, on slopes and in some small 

 depressions. Marsh growth keeps pace with subsidence in many 

 regions, and there are numerous large marsh areas along the 

 principal tidal estuaries. 



There are recent dune sands on the coast and older dunes 

 inland in part of the eastern shore region, but I have given no 

 special attention to their relations. 



RESUME OF HISTORY. 



The earliest event in the Tertiary history of which there is 

 evidence was the deposition of the Pamunkey formation in 

 Eocene times Its fine, glauconitic, highly fossiliferous sands 

 were evidently deposited in moderately deep waters containing 

 an abundant fauna. The extent of the maximum submergence 

 by Pamunkey seas and the original extent and thickness of the 

 formation are not known. As the formation represents but a 

 small proportion of the total Eocene known in other regions, 

 there either were long intervals in which this region was a land 

 surface (and this was undoubtedly the case during the deposition 

 of older Eocene formations elsewhere) or overlying formations, 

 if deposited, were subsequently removed. Consequently the 

 erosion interval between the Pamunkey and Chesapeake forma- 

 tions may have been inaugurated soon after the end of Pamunkey 

 deposition, or it may have followed much more extensive deposi- 

 tion of later Eocene formations which were removed before Ches- 

 apeake deposition. It is ascertained that the entire present 

 Coastal Plain region emerged before Chesapeake deposition and 

 there was general planing or base-levelling, but the extent of 

 uplift, the amount of tilting, and the depth of degradation which 

 followed are not known. Some light may be thrown on these 

 questions when the stratigraphy of the Pamunkey formation is 

 more accurately determined. The emergence was followed by 

 submergence during which the Chesapeake formation was depos- 

 ited. As these deposits have a known thickness of 800 feet to 

 the southeastward, and over 1,400 feet in New Jersey, and consist 

 of very fine-grained materials, and are in part diatomaceous, their 



