C EN O ZOIC HISTORY. 569 



belt open into these depressions and the larger rivers become tide 

 water estuaries in the Coastal plain. 



The formations underlying the Coastal plain province are a 

 series of widely extended sheets of gravels, sands, clays, and 

 marls lying on an east-sloping floor of crystalline rocks. They 

 are separated by unconformities and, in greater part, dip gently 

 and thicken gradually, to the eastward. They emerge at the 

 surface in succession to the westward, but there is more or less 

 overlap of the younger formations beyond the edges of the older 

 formations. The Cretaceous and Tertiary representatives are the 

 Potomac and Raritan formations, consisting of clays and sands 

 of early Cretaceous age; Magothy 1 sands and brown sandstones 

 of Maryland ; the great greensand series of New Jersey repre- 

 sented by the carbonaceous sands of the Severn formation in 

 Maryland ; Pamunkey formation consisting of glauconitic sands 

 and marls of Eocene age ; Chesapeake formation consisting of 

 clays, fine sands, and diatomaceous clays of Miocene age, and 

 the Lafayette formation consisting of gravels, sands, and loams 

 of later Neocene or Pliocene (?) age. 



On the terraces in the depressions, and on the low lands to 

 the eastward, there are deposits of gravels, loams, and sands of 

 Pleistocene age which have, in greater part, hitherto been com- 

 prised in the "Columbia formation." I have found, however, 

 that these depositions consist of two series of deposits, an 

 earlier, which lies on the higher terraces westward and is the 

 basal member eastward, and a later deposit, which lies on the 

 lower terraces, and overlies the earlier deposits eastward and 

 southward of the Potomac valley. This difference in altitude is 

 due to emergence and strong tilting from the northwestward 

 between the time of deposition of the earlier and later deposits. 

 The area of this emergence is shown by the heavier ruling in figure 

 4. The earlier deposit has not been differentiated before, but it 

 is an important and distinct member of the Coastal plain series. 

 The general relations of the various formations near the latitude 

 of Washington are shown in the fifth section on figure 3. 



1 Recently denned by Darton, Am. Jour. Sci., 3d Ser., Vol. XLV., 1893, 45 pp. 



