500 PRINCIPLES OF STRATIGRAPHY 



In general, the three principal zones given on p. 486 (the reed 

 or Phragmitetum, the sedge or Cyperacetum and the moss or Hyp- 

 netum zones) may be recognized as those which tend to succeed each 

 other in the process of filling the lake or pond, though one or an- 

 other of them may at times be absent. Toward the last the water- 

 loving trees begin to migrate into the swamp, among which in our 

 northern climes are the alders (Alnus incana, A. serrulata, A. mari- 

 tima near the coast, and A. glutinosa in western Europe), forming 

 the Alnetum zone. Elsewhere in the United States the tamarack 

 (Lari.v americana) takes the place of the alders, forming the Lare- 

 tum. In the southern states the Cypress {Taxodium distichuin) or 

 the Tupelo (Nyssa uniflora) occupies this zone, forming, respec- 

 tively, a Taxodctiim and a Nyssctum. Under and among these trees 

 a rich herbaceous flora flourishes, including ferns, sedges, the 

 Equisetum Huviatile, the pitcher plant, Saracenia, violets, Galium, 

 Impatiens and a host of others. Sphagnum, however, is absent. In 

 the cypress swamps of Florida (Stevenson-46: 7^^, etc.) and the 

 Gulf Coast, logs and woody roots are common. At New Orleans 

 the cypress and other trees were found superimposed one upon the 

 other, in an upright position, with their roots as they grew. A 

 cypress swamp dissected in cutting a canal from Lake Pontchartrain 

 showed three tiers of stumps in the 9 feet excavated, these ranging 

 one above the other. The earlier trees apparently rotted away at the 

 level of the ground before the later ones grew over the same site. 

 The peat in the cypress swamp is formed by an accumulation of 

 the forest litter, the swamps themselves being due for the most part 

 to impeded drainage on an almost level surface. The depth of the 

 material has been reported as in some cases more than 150 feet. 

 Among the largest swamps on our coastal plain are : Okefenoke 

 Swamp in southern Georgia, and the smaller Dismal Swamp of 

 Virginia and North Carolina, which covers about 500 square miles. 



In Okefenoke Swamp, which lies 50 miles from the ocean and 

 115 feet above the mean tide, the peat is about 10 feet thick, and 

 cypress stumps abound. The wetter portions are often free from 

 trees and show a luxuriant growth of cane, pickerel weed and water 

 lilies, but little or no Sphagnum. (Harper-23.) 



The Dismal Swamp (49) is only a few feet above sea-level, 

 and has a peaty deposit at least fifteen feet deep (C. A. Davis), 

 resting on Pliocenic sands. Lake Drummond lies ian its western 

 border (see ante, p. 120). Sphagnum plays only a small part in 

 the peat formation of this swamp, the canes, a grape, the bald 

 cypress (Taxodiinn distichum) and the junipers {Juniper us vir- 

 giniana) being the chief peat-forming plants. Of these the junipers 



