IMPORTANT TFPES OF PEAT MATERIAL. 11 
thus shows a convex upper surface. " Hochmoor," or " raised bog," develops 
typically in regions of high humidity or rainfall, partly on account of the 
habit of growth of the sphagnum mosses, which form the main component of 
the surface vegetation cover. " Flachmoor " represents a class of peat land 
with a flat or even a slightly concave surface. Often a distinction is made on 
the basis of chemical differences, especially the absence or presence of lime or of 
acid reaction, but this distinction is not exact. 
Acidity may arise in various ways and it may persist only for short periods 
of time. A temporary condition of acidity is common to surface peat materials 
with insufficient aeration, weathering, or disintegration, due to the presence of 
carbon dioxicl. It should be stated, however, that different peat materials may 
have different acidities, and much of the soil acidity may be potential rather 
than active. In bog types of peat, for example, acidity appears to be due partly 
to the absorbing capacity of the organic materials for bases, breaking up salts 
and liberating acids (14), and partly to the presence of end products of disin- 
tegration which are colloidal substances of an acid character. The activity of 
microorganisms and certain forms of fungi as acid builders in peat soils and 
the degree of activity and probable harmfulness have barely been touched by 
investigators (5). In the marsh types of peat, acidity is caused more fre- 
quently by the oxidation of sulphids in the underlying mineral soils or 
by drainage waters which have become acid through a variety of causes. In a 
few cases acidity is due to the long-continued application of artificial fertilizers, 
such as ammonium sulphate and others, that have been used on the soils too 
heavily. Although the cause of soil acidity and its direct or indirect effects on 
plants and on the physical, chemical, and biological conditions and processes of 
soils have been the subject of numerous investigations, any broad statement is 
unsafe at this time. 
From the standpoint of the conditions of accumulation it is desirable to dis- 
tinguish between transported peat materials, i. e., the group of peat types which 
were formed in open water and below the water level (the aquatic or alloch- 
thonous types of peat), and those which resulted from the preservation of plant 
remains on the spot actually occupied by the peat-forming vegetation units, the 
groups of peat material formed at and above the water level (the marsh, 
swamp, and bog, or autochthonous types of peat). 
The group division represents the members of a linear genetic sequence or 
vegetation series which have the same general range of controlling field con- 
ditions, e. g., the positions of the ground-water level in relation to the surface. 
Regional divisions have not been taken into account at present, since they 
represent the broader relations of types of peat material and the marked differ- 
ences which are associated with the geographic distribution of vegetation form- 
ing peat, with climate, geology, and physiographic relations. 
A type of peat material is the individual member of a group and is based 
upon differences in origin, texture, color, etc., and in botanical composition of 
such plant remains as characterize the organic material most conspicuously. 
Phases are differences in a type of peat not sufficiently well marked to justify 
a new subdivision ; they are variations in composition of plant remains, in min- 
eral matter, etc., and are in some respects correlative features of certain field 
conditions. 
From the standpoint of the vegetation units forming peat, the 
layers of plant remains preserved more or less intact are much the 
more important. They furnish a record of the development and 
structure of peat deposits, and they represent a more or less definite 
