MARYLAND GEOLOGICAL SURVEY 



ii: 



During the erosion interval which immediately preceded the deposition 

 of the Talbot formation many streams cut moderately deep channels in 

 the land surface, which on the sinking of the region again were trans- 

 formed into estuaries (Fig. 4). Across the mouths of the smaller of 

 these drowned valleys 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- 



FiG. 6. — Diagram showing later stage in advance of Talbot shore-line. 



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 

 their abode (Fig. 5). 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 whore the lagoon had been filled up to 



