MARYLAND GEOLOGICAL SURVEY 



107 



formed into estuaries (Fig. 5). Across the mouths of the smaller of 

 these drowned vallcj's the shore currents of the Talbot sea rapidly built 

 bars and beaches which ponded the waters behind them and transformed 

 them from brackish-water estuaries to fresh-water lagoons. These la- 

 goons, however, were gradually changed into marshes and possibly to 

 meadows by the inflow of detritus from the surrounding region and on 

 the new land surface thus formed various kinds of vegetation took up 



Fig. 6. — Diagram showing advancing Talbot sliore-line and ponded stream. 



their abode (Fig. 6). At first the beach-sands advanced in the lagoon 

 and filled up completely that portion of the submerged trough which 

 lay immediately beneath them, but later, as the lagoon was silted up 

 more and more with mud derived from the surrounding basin, the ad- 

 vancing beach came to rest on this lagoon deposit as a foundation and 

 arrived at length at the point where the lagoon had been filled up to 

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

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

 wind had been simply pushing forward material over the advancing front 



