IMPORTANT TYPES OF PEAT MATERIAL. 35 



The peat niateiials are characteristically a shnib or a forest litter. 

 The greater proportion consists of woody material ; roots, trunks 

 of trees, branches, bark, twigs, etc., in a tangled mass, are in all 

 stages of disintegration and more or less in such a state of preserva- 

 tion as to be determinable. In this are the remains from leaves, ferns, 

 mosses, scales, the rootlets of herbaceous plants, and fimgal hyphae 

 and spores more or less plainly recognizable. The material which 

 fills the interstices consists of semidecayed weathered tissue and 

 granular debris of great variety, comparable .in structure with 

 amorphous water-formed peat material, but free from the more 

 obviously transported drift of lacustrine and valley or estuarine 

 deposits. 



The most critical factor in origin is the position of the water table. 

 Trees instead of herbs and shrubs take possession of a wet marsh 

 or bog area and gradually become the dominant peat-forming plant 

 cover if the average water level during part of the time is suf- 

 ficiently far below the surface of peat accumulation to favor weather- 

 ing and longer periods for decay and for the products brought about 

 by beneficial bacteria and fungi. 



The deciduous-tree stage forms the end of the vegetation series; 

 it indicates that an approximate balance is maintained between the 

 amount of peat accumulation and the rise of the water level favor- 

 able for the growth of trees and that disintegration and loss of 

 plant remains go on each year at about the same rate as the addi- 

 tion to the deposit made from the mature forest. Only when there 

 is a marked and sufficiently prolonged elevation of the water table 

 from any cause will plants of other vegetation stages reappear, 

 establish themselves, and begin again the accumulation of peat 

 materials. 



Many factors may operate to affect the relationship of the water 

 level to the surface, and the resulting types of organic material may 

 vary, therefore, quite as much from climatic and other regional 

 changes as from local features or artificial obstructions. A number 

 of layers of forest litter in a peat deposit containing stumps and 

 roots of trees naturally must be interpreted to indicate an equal 

 number of modified field conditions for peat accumulation. 



The presence of roots of trees in the substratum soils of a peat 

 deposit or its bottom muds and the details of stratigraphic sections 

 are features of considerable practical importance. They point to 

 the fact that the area under consideration is in widely different con- 

 dition for peat deposition and for the disintegration of material 

 from that of filled basins. Originally in a land area with drainage 

 well established the water table became elevated, probably through 

 varying coastal subsidence, accompanied perhaps by irregularities 



