MARYLAND GEOLOGICAL SURVEY IVJl 



seaward. At Chesapeake Beach a ditoli has been cut through one of 

 these beaches whicli shows a continuous deposit of chiy from a lagoon 

 swamp passing out under the beach to the Bay beyond. The waves are 

 thus caught, as it W(>re, in the act of eroding the upper portion of the 

 lagoon deposit. 



From a large body of data gained from over a wide area, it is evident 

 that the erosion which occurred during the interval between the eleva- 

 tion of the Talbot terrace and the present subsidence of the coast was 

 sulTicient to permit streams to cut moderately deep valleys in the former. 

 It would then appear that as the region was gradually lowered again 

 beneatii the present ocean the upper portions of the stream-channel in 

 time passed below wave-base and whatever has collected in them since 

 that period will be preserved beneath the advancing sea as a more or 

 less fossiliferous clay lens apparently unconformable beneath beach 

 debris. 



The barrier beaches which exist at intervals along the Atlantic coast 

 of New Jersey, Delaware, Maryland, Virginia, and southward show us 

 how portions of the ocean-bed, which were formerly bathed by salt water 

 and sustained a marine fauna, are now converted to lagoons behind 

 barrier beaches, and have passed over in varying degrees to brackish- 

 water conditions bearing estuarine faunas. 



Similar deposits to those just described have been seen by the author 

 along the Rappahannock River, especially at Mosquito Point, and there 

 is no reason to doubt that they occur in many other places along Chesa- 

 peake Bay and its estuaries, within the State of Virginia. From analogy, 

 it would be expected that similar deposits would he discovered along 

 Delaware Bay whore conditions must have been identical with those which 

 prevailed in Chesapeake Bay. That such deposits do occur along the 

 shores of the Delaware there can be no doubt. The most noted of these 

 is at Fish House on the New Jersey side of the Delaware River a few 

 miles above Philadelphia. 



