IMPORTANT TYPES OF PEAT MATERIAL. 11 



thus shows a convex upper suii'uce. " Hoehiuoor," or " raised bog," develops 

 typically in regions of high humidity or rainfall, partly on account of the 

 hal)it 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 tlie absence or presence of lime or of 

 acid reaction, but this distinction is not exact. 



Acidity may arise in various wa.vs and it mny 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 dioxid. 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 tj'pes 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 applicati(jn 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, geologj^ 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. Thej' furnish a record of the development and 

 structure of peat deposits, and they represent a more or less definite 



