MARYLAND GEOLOGICAL SURVEY 



109 



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. 7) which represents a stage where the waves have so far 

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

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

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

 advancing beach. The transverse section shows what is left of the 

 lagoon deposits of mud carrying truncated stumps of cypress and other 

 trees which happened to be buried deep enough to escape the destructive 

 powers of the breakers. The broken line indicates the outline of the clay 

 lens. Fig. 8 is a section through the same region made at right angles 



B 



D 



Fig. 8. — Ideal section showing advance of Talbot shore-line. 



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 mud which reached out to 

 them under the beach veneer. At C the waves have succeeded in cutting 

 down the lagoon deposit to wave-base and have left behind a thin veneer 

 of sand and gravel as the sinking land carries it 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 out toward A. 



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

 brackish-water organisms are understood to have been formed in a 

 somewhat different manner. The lower portion . carrying the marine 

 organisms points to salt-water conditions and contains remains of sea 

 animals which live to-day along the Atlantic coast. At the time when 



