108 



THE GEOLOGY OF ST. MARY S COUNTY 



but now the mud deposit in the lagoon had actually reached the level of 

 wave-work and had transformed the lagoon from a pond to a marsh or to 

 a meadow, the breakers attacked the upper portion of the lagoon deposit 

 and eroded it down to the level of wave-base as rapidly as they could 

 reach it from under the superficial veneer of the beach-sands. Cypress, 

 cat-tails, sedges, and other vegetation which had taken up their abode 

 in the marsh would be overwhelmed with detritus by the advancing bea^ h 



Fig. 7. — Diagram showing later stage in advance of Talbot shore-line. 



and a little later be destroyed by the breakers. In this way all traces 

 of life must be removed from the deposit except such as happened to 

 occupy a position lower than wave-base. One, therefore, finds preserved 

 in the clay water-logged trunks and leaves, nuts, etc., and roots of huge 

 trees like the cypress. The area over which the waves had removed the 

 upper portions of the lagoon deposit can be determined not only by the 

 presence of truncated stumps but also by the character of the contact. 

 Here there is a sharp division between the clay and the overlying sand 

 and gravel while the area over which the beach advanced without cutting 



