«9>i] STEVENSON— FORMATION OF COAL BEDS. 595 



of fallen trunks, twigs and leaves. Shaler's plates from photographs 

 taken in this forested swamp show the conditions thoroughly. 



Shaler"'-' has described the peculiar modification of structure 

 characterizing the bald cypress. This is the greatest of the conifers 

 east from the Rocky mountains and it is the most stately of all the 

 trees on the eastern half of the continent. On dry ground or where 

 there is no water during the summer half of the year, it shows no 

 peculiarities ; but where it lives in swamps, flooded during the grow- 

 ing season, the roots give ofif excrescences which project above the 

 water, their height depending on the depth of water. These " knees " 

 are subcylindrical and are crowned by a cabbage-shaped expansion 

 of bark, rough without and often hollow within. Whenever these 

 knees become permanentl}' submerged during the growing season, 

 the tree dies ; as was proved in the New Madrid area, where, during 

 the 1811 to 1813 earthquakes, the land sank permanently. In Reel- 

 foot lake, within Kentvicky and Tennessee, thousands of these long 

 cypress boles still stand in the shallow waters, though 70 vears have 

 passed since the slight submergence of their knees. The eitect of 

 drowning is shown on a plate in the work previously cited. Many 

 dead stems of cypress rise above the surface of Drummond lake, 

 which is only a few feet deep. Lesquereux thought that these were 

 once part of a floating forest. 



Okefinokee swamp in southern Georgia is not wholl}- a forested 

 swamp. It is larger than Dismal Swamp and more difficult to study. 

 Harper^'" succeeded in penetrating it to a distance, all told of about 

 18 miles. Here and there are islands, raised a little above the swamp 

 level, at times not more than 2 feet, often less. On those the slash 

 pine and the black gum grow, while all around are sphagnous bogs 

 in which are slash pine, as well as swamp cypress, with sedges, ferns, 

 sundews, and pitcher plants. Pines are wanting where the muck is 

 more than 4 feet deep, but the cypress grows densely until the depth 

 exceeds 6 feet. Where that depth is exceeded, no trees are found 



"" N. S. Shaler, " The American Swamp Cypress," Science, O. S., Vol. 

 II., 1883, pp. 38-40. 



""R. M. Harper. "Okefinokee Swamp," Pop. Sci. Monthly, Vol. LXXIV.. 

 1909, pp. 596-613. 



193 



