IMPORTANT TYPES OF PEAT MATERIAL. 29 
The material disintegrates rather poorly and becomes brittle when 
overdrained, breaking down into a dust, or mull. Older layers are 
blackish in color and appear more or less structureless. 
The type is more generally a transition feature to the bog group 
of peat materials; it is found in peat deposits in the Northwestern 
States and seems to occur there in considerable thicknesses. In the 
Central and Eastern States it is found only in layers and pockets of 
irregular size, heavily admixed with the plant remains of species of 
Carex, Phragmites, and other peat-forming plants. Tables I and II 
contain the more important physical and chemical data for this type 
of peat. 
THE BOG GROUP OF PEAT MATERIALS. 
Types of peat material (autochthonous) from bog-meadow and 
bog-shrub stages of a vegetation series in wet places, with the water 
table near or slightly below but rarely above the surface. 
The plant remains are characteristically spongy and porous or 
matted-fibrous to wickerlike peat, somewhat resistant to disintegra- 
tion, reddish, yellowish, and deep brown in color. The interstices are 
filled with a macerated debris in varying proportions, often soft and 
oozelike, in which fragments of cell complexes are usually well 
enough preserved to be determinable. The resinous constituents and 
the threadlike rusty brown root fragments of heaths with mycelial 
fungi are an important factor in lending the specific character and 
value to this group. In transition stages the finer debris or ground 
mass forms a considerable portion of the material, with intergrada- 
tions from structureless plastic-appearing substances discerned with 
difficulty to clearly recognizable fibrous and woody fragments. 
The materials are derived from vegetation units which appear first 
as scattered, more or less localized plant associations in the marsh 
stages of a peat deposit. It seems that the succession of marsh to 
bog has taken place far more frequently than recognized hitherto, 
since sections through the profile of the lower layers of peat deposits 
in many localities show clear evidence that the area was formerly 
occupied by marsh vegetation. Quite similar stratigraphic succes- 
sions leading from marsh to bog recorded in the peat deposits of 
European moors have been recognized in this country. In lacustrine 
deposits, however, bog vegetation appears often as foreland com- 
munities and immediately following the semiaquatic stages of a vege-, 
tation series after the accumulation of macerated, structureless, water- 
formed peat has reached nearly to the water level. By means of 
much-branched interwoven underground stems and fibrous rootlets 
they border open water or completely surround it as a floating mat, 
which rises and falls with the seasonal variations in the water table 
