128 THE PLIOCENE AND PLEISTOCENE DEPOSITS OF MAKYLAND 



stituting one, and those containing marine and brackish-water fossils 

 the other. 



In brief, the clays carrying plant remains are regarded as lagoon de- 

 posits made in ponded stream channels and gradually buried beneath 

 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 



Fig. 6. — Diagram showing pre-Talbot valley. 



formed behind a barrier beach and gradually buried by the advance of 

 that beach toward the land. Taking up the first class of deposits in more 

 detail, they are interpreted in the following manner : 



During the erosion interval which immediately preceded the deposition 

 of the Talbot formation, many streams cut moderately deep channels in 

 the land surface which, when the region began to sink again at the open- 

 ing of Talbot time, were gradually transformed into estuaries (Fig. 6). 

 Across the mouths of the smaller of these drowned valleys the shore cur- 



