MARYLAND GEOLOGICAL SURVEY 



187 



engaged the attention of the author until it appeared that the appar- 

 ent unconformity with the Talbot, although in a sense real, does not, 

 however, represent an appreciable lapse of time and that therefore 

 the clay lenses are actually a part of that formation. In order to un- 

 derstand more clearly what is believed to have taken place, these clay 

 deposits should be divided into two groups, those which carry plant 

 remains constituting one, and those containing marine and brackish- 



Fig. 8. Diagram showing pre-Talbot valley. 



water fossils the other. Such as are devoid of fossils may belong to 

 either one of the groups according to their situation but probably 

 more frequently belong to the latter. 



In a word, the clays carrying plant remains are regarded as lagoon 

 deposits made in ponded stream-channels and gradually buried be- 

 neath the advancing beach of the Talbot sea. The clays carrying 

 marine and brackish-water organisms are believed to have been at 

 first off-shore deposits made in moderately deep water and later 

 brackish-water deposits made behind a barrier-beach and gradually 



