8 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 varving 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 alga?. A few pollen grains, diatoms, and attrite organic 
debris 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, F, 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- 
erate proportion of this finely divided material embedded in fibrous 
or woody layers of peat serves as a binder, giving additional compact- 
ness. 
