206 



the leaves were buried. The leaves were buried at near sea 

 level, or if the water was a few feet deep there was evidently 

 only the finest detrital materials being brought down by the 

 valley stream, and this quiescent condition continued during 

 the time represented by the lo feet of clay overlying the leaf- 

 bearing layer. Subsidence with quickening erosion followed and 

 the surface of the estuary finally rose to at least 40 feet above 

 the plant layer. This was followed by reversal of movement 

 which finally resulted in bringing the surface at least 20 feet above 

 sea level. 



The recognizable plants are all recent species most of which 

 are common Pleistocene types. Fraxinus americana has not 

 heretofore been recorded in the Pleistocene but it and all of the 

 other forms are still common in the Potomac valley except the 

 Bald Cypress, which is no longer found in the immediate vicinity, 

 although several cypress swamps are still present farther south 

 in Charles County. The Liriodendron is represented by a 

 characteristic juvenile leaf such as is rarely found fossil. 



Order CONIFERALES 

 Family PINACEAE 

 Genus Taxodium L. C. Richard 

 Taxodium distichum (Linnaeus) L. C. Richard 



The remains of the bald cypress are very common in American 

 Pleistocene deposits from New Jersey and Maryland southward, 

 where they are represented by the deciduous twigs, cone scales, 

 seeds, aments, and stumps with the characteristic "knees." 



A few of the deciduous twigs occur in the present collection. 



Order FAG ALES 



Family FAGACEAE 



Genus Fagus Linnaeus 



Fagus Americana Sweet 



The beech is widely distributed in the fluvial Pleistocene 

 deposits of the Southern States, where it is commonly represented 



