IMPORTANT TYPES OF PEAT MATERIAL. 15 



and to a smaller extent Typlia, Phragniites, and other genera 

 more typical of the later grass and sedge vegetation imits. 

 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 gTowth 

 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 b}^ 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- 



