IMPORTANT TYPES OF PEAT MATERIAL. 21 



Especially interesting in this connection are the marly and diato- 

 maceoiis accumulations, which on account of their importance are 

 treated here as subtypes. 



CharaceouH aubtyfe. — Structureless, mainly calcareous plant re- 

 mains, predominantly the deposition of calcium carbonate by green 

 algae, such as the stoneworts Chara and Nitella; usually comminuted 

 granular fragTnents, soft, friable, and cream colored to white when 

 pure, yellowish to dark rustj^ red according to the amount of iron 

 present, gi'ayish brown to black and granular when admixed with 

 herbaceous plant remains. 



Shell-marl phases are quite common among Aarious types of peat, 

 but the shell remains from mollusks are not an important factor in 

 the production of the larger or more extensive accumulations of 

 marl. Inclusions, such as calcareous tufa, concretions and nodules 

 caused by blue-gi'een algae or by bacterial precipitation, and flaky in- 

 crustations on semiaquatic plants, mosses, rhizomes of herbaceous 

 plants, and a form of fine tubular material derived from mats of 

 stonewort buried essentially intact, are occasionally found embedded 

 in the macerated types of peat material. Most of the calcareous sub- 

 type of plant remains is covered with herbaceous organic matter, 

 but outcrops and layers between beds of peat material are frequent in 

 level valleys. 



Extensive deposits of marl and of marly peat materials of other 

 types occur mainly in regions underlain by rock formations contain- 

 ing limestone and in areas where streams, underground and spring 

 waters, or the soil material adjacent to and underneath a peat area 

 are derived from calcareous drift. 



Sandy, argillaceous, ferruginous, phosphatic, and peaty marls owe 

 their names to their obvious admixture. Marly phases of peat are as 

 a rule granular, grayish brown to blackish gray in color, and inclined 

 to be high in available nitrogen when under cultivation. To re- 

 store a proper balance in the ratio of plant food constituents, they 

 therefore should not be treated with nitrogenofts fertilizers. Where 

 the amount of lime is too high, crops tend to become chlorotic and are 

 susceptible to nutritional disturbances. 



Beds of pure marl are used in the manufacture of cement, and they 

 furnish lime of value as an agricultural fertilizer. 



DiatoTnaceoiis subtype . — Structureless, mainlj^ siliceous material 

 from plant remains consisting of diatomaceous shells admixed with 

 a varying proportion of sponge spicules, spore cells, macerated or 

 fibrous plant material, and drift debris ; light gray in color and com- 

 pact but of very little weight in proportion to its air-dry bulk ; per- 

 vious when free from impurities; blackish gray and plastic to sticky 



