6 BULLETIN 1419, U. S. DEPARTMENT OF AGRICULTURE 
The use of key letters, indicated in Plate l,with numbers correspond- 
ing to the thickness of each layer, would serve a similar purpose'. 
Attention also needs to be given to rainfall and general climatic 
conditions. Weather and climate influence not only the growth of 
crops and a variety of plant diseases common to peat lands, but 
they affect also the air-drying of layers of peat, the control of the 
water level, and the length of a practical working season for peat 
products. With the necessary information concerning peat profiles 
and environmental conditions and requisite economic data as a basis, 
it is possible to make certain reasonable assumptions as to the avail- 
ability of different materials, the appropriate method of production, 
and the probable cost or profit per acre or per ton. 
SELECTION OF PEAT LANDS FOR ECONOMIC USES 
For agricultural as for other industrial uses, the selection of desir- 
able peat land should be based on accurate and definite information 
as to the structure of the peat area and the relationships involving 
the water supply and the mineral substratum. The outstanding 
features of these principal conditions are covered more fully in the 
following pages. Attention must be focused on them because they 
are of fundamental significance, and they interfere more or less with 
each other. They form the principal task of modern peat investi- 
gations, and they exercise a limiting influence upon necessary and 
ordinary operations, such as methods of drainage, tillage, crop rota- 
tion, fertilizing, and all other forms of utilization of peat deposits. 
With these characteristic conditions identified and understood, the 
various peat-using interests will have competent data on which to 
work, with a measure of control that previously has been impossible. 
Presently, no doubt, regional land planning, as well as colonization 
projects and the like, will be based upon dependable information of 
the sort indicated, 
CHIEF DIFFERENCES BETWEEN LAYERS OF PEAT 
Layers of peat are the basis and the units of peat-land classification. 
They are identified by reason of the differences in kind and quantity 
of plant remains from which they are formed. Microscopic exami- 
nation indicates clearly the plant remains of which the three primary 
divisions of peat — the sedimentary precipitate (more or less gelati- 
nous) , the fibrous, and the woody layers — are composed. This is true 
also of the less clearly defined mixed layers of peat. The transfor- 
mation of the surface vegetation to peat, and even to lignite and coal, 
seemingly is accomplished without any great change in the botani- 
cal structure of the buried plant tissue. In most instances the net- 
work of roots or of moss plants, the different proportions of spores, 
pollen grains, and finely divided bits of plant tissue, as well as the 
cuticular, resinous, and woody fragments of varying sizes, are found 
well preserved in the respective layers of peat. The evidence of 
European investigators as to the development of forests in postgla- 
cial times is based on the method of quantitatively analyzing the 
pollen grains identified in different peat materials. 
According to their origin, layers of peat represent the plant remains 
of social units of vegetation. They are distinctive products from 
