Maryland Geological Survey 161 



small bodies of water. This would be the conclusion even if there were 

 not such startling, almost complete resemblance between the diagram of 

 this sediment (H, p. 169) and that of the delta in the Lagoon of Thau 

 (I, p. 170). The conditions I think may have been exactly those repre- 

 sented now by one of the submerged stream mouths forming the estuaries 

 of Chesapeake Bay, or perhaps by the nearer shore portions of the main 

 body of the bay near the point of discharge of some stream. 



The abundance of fossils encountered here for the first time in the 

 sediments analyzed conforms to such an assumption. Their good preser- 

 vation leaves little doubt that they did live in place and were not trans- 

 ported. 



The abundance of fossils encountered here for the first time in the 

 this type as in sample 4. 



A peculiar feature is the low percentage of heavy minerals (about 

 4.5%). But inspection of Thoulet's analyses from the Gulf of Lyon shows 

 that this is so variable a feature that it must be largely dependent on the 

 original composition of the material supplied. 



The field relations of this bed require some special mention. The bed 

 lies directly on a white Potomac clay, with a somewhat irregular surface 

 of contact but without any evidence of a coarser basal portion. This seems 

 to confirm the above interpretation. For any swiftly moving water 

 with strong transporting power, or any body of water with strong wave 

 action, must in its progress over a land surface leave a deposit of sorted 

 coarse material, if such is available. Now, such material is available in 

 the Potomac bed under consideration, so that if there had been strongly 

 agitated water this coarse material must have been selected and deposited 

 while the finer material was carried into more quiet water. Then as sub- 

 mergence progressed, finer material would come to overly the coarser with 

 a gradual transition. But if a relatively quiet body of water, deriving 

 its material laterally from some nearby stream emptying into it, trans- 

 gressed over a surface of such white clay, it would, it seems to me, have 

 only finer material to deposit and therefore put such material down as a 

 bottom layer. Even here, however, slight wave action and therefore slight 

 sorting might be expected, unless the shore were lined with water plants 



