MARYLAND GEOLOGICAL SUETET 111 



and still others have reached the advanced stage of swamps or meadows 

 in which various types of vegetation are flourishing. In addition to the 

 usual undergrowth whicli is found in wet places, the cypress has taken 

 up its abode in these bogs and has converted some of them into cypress 

 SM'amps. For great stretches along the shore the advance of the sea is 

 indicated by well-washed cliffs while in other places the waves are found 

 devouring beds of clay which are situated immediately in front of lagoon 

 swamps and separated therefrom by nothing but a low superficial beach. 

 These clay beds invariably lie at and below water-level, are very young 

 in age, and evidently pass directly under the beach to connect with the 

 lagoon-clay beyond. This interpretation is made the more certain by 

 the presence of roots in the wave-swept clays which but a short time 

 before belonged to living plants identical with those now flourishing 

 beliind the beach, and point to a time not far distant when they also 

 were a part of the lagoon swamp behind a beach situated a little farther 

 seaward. At Chesapeake Beach a ditch has been ciit through one of 

 these beaches which shows a continuous deposit of clay from a lagoon 

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

 thus caught, as it were, 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 

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

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

 beneath 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 



