A FEW WORDS ABOUT COAL. 299 



dense is the marginal belt of reeds and brushwood. It 

 may be affirmed that generally in the 'cypress-swamps* 

 of the Mississippi no sediment mingles with the 

 vegetable matter accumulated there from the decay of 

 trees and semi-aquatic plants. As a singular proof of 

 this fact, I may mention that whenever any part of a 

 swamp in Louisiana is dried up,^during an unusually hot 

 season, and the wood is set on fire, pits are burned into 

 the ground many feet deep, or as far down as the fire 

 can descend without meeting with water ; and it is then 

 found that scarcely any residuum or earthy matter is 

 left. At the bottom of all these 'cypress-swamps' a 

 bed of clay is found, with roots of the tall cypress, 

 just as the under-clays of the coal are filled with 

 stigmaria the roots of the ancient forest-trees called 

 sigillaria.* 



It will be seen that the circumstances here con- 

 sidered dispose of the theory once a favourite one 



* It is not quite certain to what type of vegetation these trees be- 

 longed. They were formerly supposed to be tree-ferns, but some are 

 found to have had long straight leaves, unlike those of ferns. The 

 reader will probably remember that, after describing the sigillaria, the 

 author of Vestiges of Creation describes the stigmaria as a distinct 

 plant. ' Among the most remarkable of the leading plants of the coal 

 era, without representatives on the present surface, are the sigillaria, 

 of which large stems are very abundant, showing that the interior has 

 been soft, and the exterior fluted, with separate leaves inserted in ver- 

 tical rows along the flutings ; and the stigmaria, a plant apparently 

 calculated to flourish in marshes or pools, having a short, thick, fleshy 

 stem, with a dome-shaped top, from which spring branches of from 

 twenty to thirty feet long.' These branches were, in reality, the roots 

 of the sigillaria. The mistake is a very natural one, since the coal- 

 seam actually separates the trunk of the tree from its roots. Some, 

 however, have since been found attached to the base of the tree-stumps. 



