64 TREE ANCESTORS 



In North America the forests shrank southward before the ice 

 sheets and spread northward during the Interglacial periods. At 

 those times of pressure from the north on the plant populations 

 of eastern North America — forests had already practically disap>- 

 peared from what is now and was then the plains country — many 

 tree species ranged southward along the highlands to Central 

 America. Among these southward spreading migrants was the 

 cypress which left a species stranded there as it were when ch- 

 matic changes occurred in the region which today separates the 

 range of the bald cypress from that of the Mexican cypress. 



A very large number of fossil swamp deposits where once were 

 cypress bays have been uncovered by artificial excavations or by 

 natural erosion of sea cut scarps or river cutting in the Pleistocene 

 deposits of the Coastal Plain. These old cypress swamps, often 

 •with the stumps of trees of great size, 8 to 10 feet in diameter, are 

 especially comm^on in the tidewater country of Maryland and 

 Virginia. The remains of one of these cypress swamps has been 

 exposed by recent cutting of the Rappahannock River a short 

 distance above the town of Tappahannock, Virginia. The peat 

 which represents the old swamp muck is exposed for a thickness 

 of 4 or 5 feet and is overlain by from 15 to 20 feet of sand and clay. 

 Associated with the cypress stumps, cone scales, and more rarely 

 leaves and catkins, are often found hickory and beech nuts, grape 

 and gum seeds, beetle wings and insect galls, and other evidences 

 of the contemporaneous life. 



Another Pleistocene cypress swamip on the Rappahannock 

 River near Waterview, shows the old stumps in their peaty matrix 

 planed off and covered by thick beds of sand — a readable record 

 of a once sinking area where the estuary waters advanced over 

 the swamp, killing the seedlings and wasting the old trees, the 

 surface having been eventually scoured smooth by the waves that 

 deposited the sands layer upon layer with the continued subsidence. 

 Subsequently elevation succeeded subsidence and in modern days 

 the river is engaged in cutting away this fragment of Pleistocene 

 history. 



