IMPORTANT TYPES OF PEAT MATERIAL. 15 
and to a smaller extent Typha, Phragmites, and other genera 
more typical of the later grass and sedge vegetation units. 
The maximum depth at which a number of the water plants and semi- 
aquatics can grow and accumulate as peat in situ varies with the 
clearness and temperature of the water, but it rarely exceeds 15 feet 
(5 meters) below the surface of the water level. Under conditions 
which accelerate the disintegration of organic material, as in regions 
having a moderate winter season or which give rise to ground water 
colored brown from the presence of suspended and dissolved organic 
debris, the filling of depressions is chiefly from the bordering marsh, 
bog, or swamp vegetation units. 
Three clearly distinguishable types of peat derived from this vege- 
tation are encountered frequently in the same deposit, which differ 
from one another throughout in texture, color, composition, shrink- 
age, and other characteristics. In some deposits, however, these dis- 
tinctions intergrade or the material occurs wedged in as a ground 
mass among the interstices of woody or fibrous types of peat, or it 
may be wholly absent. 
The peat mass composed of very small particles possesses many of 
the properties of a colloid and is on that account of the greatest im- 
portance in the problem of dewatering the material for the growth 
of crops or for manufacturing purposes. It is difficult to remove the 
water content to below 80 per cent, and when dry these types of peat 
may form gaping cracks and may shrink to one-fourth and even 
to one-eleventh of their original profile dimension. They are easily 
tilled, but under cultivation in open crops readily become finely 
granular, forming a dustlike powder, almost impervious to water, 
probably caused by the absorption of air. Loss in yields from wind 
erosion and plant diseases appears to be a detracting feature in this 
group unless provision is made for windbreaks, irrigation, or for a 
cropping system that combines or alternates with grasses, small 
cereals, and broad-leaved crops. The use of sand by mixing it or by 
covering the peat material with a layer of sand 6 to 8 inches (15 to 
20 cm.) thick should be practiced with caution; the method increases 
in most cases the yield as well as the possibility for growing a greater 
variety of crops, including truck, cereals, and other staple crops, but 
losses have been reported due to the selection of unfavorable deposits 
of material. 
Some of the materials are noteworthy because of the relatively 
high nitrogen content, while others contain more of the waxy, resin- 
ous, and other ether and alcohol soluble organic debris (see Table I) 
from shrubby or herbaceous evergreens. On account of the greater 
resistance to oxidizing and other agents and to bacterial action, this 
plant residue disintegrates slowly and tends to accumulate in con- 
