118 



THE GEOLOGY OF CALVERT COUNTY 



the level of wave-base or higher. When this place was reached another 

 process was added to that of beach andvance. Heretofore the waves and 

 wind had been simply pushing forward material over the advancing front 

 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 beach 

 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 



B 



^^ __^ ..^^ -_^ 



Fig. 7. — Ideal section showing advance of Talbot shore-line. 



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 

 would be indicated by a partial mingling of the beach material with 

 lagoon mud. 



A still later stage in the process is illustrated in the accompanying 

 diagram (Fig. 6) which represents a stage where the waves have so far 

 advanced as to largely destroy the original stream channel. A small 

 portion of the old lagoon still exists at the head of the swamp but its 

 lower portions have long since been submerged and covered over by the 



