BULLETIN 1419, U. S. DEPARTMENT OF AGRICULTURE
could be made by uniform methods. To be definitely useful for
practical purposes the data need to be systematized. The differences
of various peat layers and their corresponding effects upon agricul-
tural and industrial operations should be expressed on a common
basis for comparison.
Varieties of the jellylike, sedimentary layers of peat are shown in
Plate 3. They are also designated by the digit 1 in the profile series
in Plate 1. Of the specimens shown in Plate 3, sample A represents
a dark-brown, fine-textured, moist, sedimentary peat over a bed of
shells and Chara marl. The plant remains are of microscopic size
and in varying states of preservation. The predominant organic
constituents are derived from aquatic vegetation, plankton, pollen,
spores, and from the degradation of woody and resinous tissues.
Plate 3, B, shows an air-dried pulpy peat of sedimentary origin which
contains iron salts in varying concentrations. It is not uncommon to
find an abundance of calcium-sulphate crystals in the material of some
unproductive peat areas. This condition is shown in Plate 3, C, an
air-dry, dark reddish brown sedimentary peat. The clusters of cal-
cium-sulphate crystals were formed by the neutralization with ferrous
sulphate and sulphuric acid with lime. * These two substances are oxi-
dation products of marcasite (iron sulphide or pyrites). Plate 3, D,
shows a bluish green, orange, and maroon colored, plastic moist peat,
embedded in shells and Chara marl. This material is not an impor-
tant constituent, either of existing open-water deposits or of sedi-
mentary types of peat; it is found as a surface layer under shallow
open water, and contains gelatinous nodules formed by colonies of
blue-green alge. A few pollen grains, diatoms, and attrite organic
débris of dark-brown color are present. Plate 3, E, represents an
air-dry, blackish brown, rubbery, colloidal peat of sedimentary origin,
showing cracks from irregular shrinkage. The plastic material con-
tracts into a dense and hard mass as the moisture content diminishes
by evaporation. It rarely splits along definite horizontal lines, but
breaks up usually with a conchoidal or subconchoidal fracture. Plate
3, FF, is typical of a mixed phase of fine-textured, sedimentary, air-
dry peat, with embedded fibrous material derived from reeds. These
mixtures are capable of holding appreciable quantities of unfree
water and under suitable conditions tend to hasten decay. Some of
the layers are noteworthy because they contain quantities of micro-
scopic siliceous material from diatoms and sponge spicules. These
are popularly known as itchy muck.
Sedimentary types of peat consist mostly of a fine-textured, non-
fibrous fraction of organic matter. They have a high absorbing
power for soluble salts and retain large quantities of unavailable
water. This probably explains their colloidal character, more or less
elastic when the moisture content, diminishing by evaporation,
reaches a definite critical stage. Water-soaked layers of sedimentary
peat material give way under pressure; but when drained they con-
tract more and more into a dense mass, becoming hard upon air dry-
ing. Because of the irregular shrinkage, a sedimentary layer may
show vertical cracks and fissures. When exposed to alternate mois-
ture and drying, it crumbles and assumes a granular form. A mod-
arate proportion of this finely divided material embedded in fibrous
or woody layers of peat serves as a binder. giving additional compact-
NeKS
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