10 BULLETIN 802, U. S. DEPARTMENT OF AGRICULTURE. 
immaterial; one is as important as the other, for each is correlated 
with the other. Any attempt toward clarity of terms and state- 
ments, any definite determination of criteria for the classification or 
selection of peat deposits and their materials for agricultural or 
manufacturing purposes depends upon and includes a twofold qualifi- 
cation: (1) The botanical composition and stage of disintegration of 
the peat materials in a deposit and (2) the controlling basic factors in 
field conditions. These constitute an effectual limitation to the de- 
gree of success obtainable. The numerous abortive attempts at 
utilization have invariably followed from neglect of one or the other 
of these essential qualifying factors. Upon the recognition of these 
depends whether the farmer and the technician are to work by chance 
or on scientific lines. 
It is not within the scope of this paper to deal with an ecological 
account of peat-forming vegetation units, of the character of initial 
stages, or of series of developmental stages arising in an area of a 
particular region. These have been discussed elsewhere in consider- 
able detail (4; 5, p. 220-262). 
The object of these notes is to call attention to the following terms 
and definitions: 
Peat is an accumulation of plant remains in various stages of disintegration 
or maceration, laid down in a definite manner according to imposed modifying 
field conditions. For statistical purposes and for reasons of common scientific 
interest the use of the term " peat deposit " should be limited to an accumula- 
tion of plant remains of at least 8 to 10 inches (20 to 25 centimeters) in thick- 
ness when compact and well shrunk. In this accumulation the surface layer 
of living native vegetation or deposits containing more than 40 per cent of 
mineral matter must not be included. 
Muck is a phase of surface peat material which occurs under topographic con- 
ditions permitting extensive weathering and the accumulation of large amounts 
of silt and clay. 
Humus. — No definition can be given at present, since the well-known defects 
in the usual methods of humus determination have made it clear that the use 
of the term in its present meaning is not advisable either in statements relat- 
ing to soils or fertilizers. 
Marsh (fen), bog, heath, and swamp are terms used largely on account of 
the well-marked physiognomy of vegetation which they represent and because 
they are common names in many languages.' The plant remains of each group 
accumulating as peat are among the most distinctive of peat materials, and the 
field conditions of each have a more or less differentiating character. The de- 
posits are quite variable in origin and structure, but their structure is primarily 
dependent on the form of the land surface on which they are found and upon 
the height of the water table while they are formed. They are dealt with later. 
The words " marsh " and " swamp," on the one hand, and " bog " and 
"heath," on the other, correspond in a very general way with the terms 
" Flachmoor " and " Hochmoor " used by most European writers. The line of 
distinction and the transition between them is, of course, nothing like as sharp 
as the terms would seem to indicate except in regions having climatic condi- 
tions where they reach their best development. " Hochmoor " is applied, as a 
rule, to a class of peat land which rises from the edges toward the middle and 
