IMPORTANT TYPES OF PEAT MATERIAL. 35 
The peat materials are characteristically a shrub 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 fungal hyphse 
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 
