MARYLAND GEOLOGICAL SURVEY 131 



but also by the character of the contact itself (Plate XVI, Fig. 1, and 

 Plate XVII). At this line 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 Figure 8, which rep- 

 resents a stage where the waves have so far advanced as to largely destroy 

 the original stream channel. A small portion of the old swamp still 

 exists at the head of the valley, but its lower portions have long since been 

 submerged and either destroyed or covered over by the advancing beach. 

 (Plate XXI, Fig. 2.) The transverse section illustrates what is left of 

 the lagoon deposits of mud carrying truncated stumps of cypress and 



Fig. 9. — Ideal section showing advance of Talbot shore-line. 



■other trees which happened to be buried deep enough to escape the de- 

 structive powers of the breakers. The broken line indicates the border 

 of the clay lens. Figure 9 is a section through the same region made at 

 right angles to the one just described. At D the breakers are forcing 

 forward the beach upon the meadow. Just off from the beach the waves 

 have swept away the sand and are eroding on the lagoon deposit which 

 reached out to them under the beach veneer. At C the waves have suc- 

 ceeded in cutting clown the lagoon deposit to wave base and have left 

 behind a thin veneer of sand and gravel as the sinking land carries it 

 down below the reach of the waves. At B the lagoon deposit was not 

 thick enough to reach the zone of wave erosion and simply grades up into 

 a thick deposit of sand and loam which passes outward toward A. 



The second category of clay lenses, namely, those carrying marine and 

 brackish- water organisms are believed to have been formed in a somewhat 



