120 THE GEOLOGY OF CALVERT COUNTY 



but there is no indication of an appreciable time-lapse between the 

 clay and the oyster-bed on the one hand and the overlying sands and 

 gravel on the other, and the sea which eroded the clay to a fixed level 

 immediately afterwards overspread the surface of the same with a veneer 

 of beach sand. There is, therefore, no time break indicated by this 

 unconformity and the lenses of swamp-clay as well as those carrying 

 marine and brackish-water organisms are to be looked upon not as 

 records of elevation and subaerial erosion but as entombed lagoon- 

 deposits made in an advancing sea and contemporaneous with the other 

 portions of the formation in whose body they are found. 



The hypothesis here advanced is based on and reinforced by many 

 observations along the present shores of the Atlantic Ocean, Chesapeake 

 Bay, and its estuaries. Each step in the process described above is there 

 illustrated and some of them are met with again and again. 



As one passes along the shores of Chesapeake Bay and of the rivers which 

 flow into it, stream channels are continually met which have arrived at 

 more or less advanced stages in the above-mentioned process. Some are 

 in part converted into lagoons, by bars built across their mouths, others 

 show partial filling by mud washed in from the surrounding country, 

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

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

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

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

 swamps. 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 

 behind 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 



