106 THE GEOLOGY OF ST. MART'S COUNTY 



stituting one, and those containing marine and brackish-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 beneath 

 the advancing beach of the Talbot sea. The clays carrying marine and 



Fig. 5. — Diagram showing pre-Talbot valley. 



brackish-water organisms are believed to have been at first oS-shore 

 deposits made in moderately deep water and later brackish-water de- 

 posits made 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 believed to have been formed 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 on the sinking of the region again were trans- 



