14 BULLETIN 802, U. S. DEPARTMENT OF AGRICULTURE. 
with, crops for the purpose of operating the peat deposits at their 
maximum efficiency. Lack of knowledge of the efforts made along 
these lines by European workers over a period of more than a century 
is directly responsible for the failure which, the attempts in this 
country Lave met. 
A TENTATIVE CLASSIFICATION OF IMPORTANT TYPES OF PEAT 
MATERIALS. 
In the following classification of peat materials all those data of a 
physical and chemical nature resulting from investigations of Euro- 
pean types of peat have been summarized in Tables I and II which, 
in the opinion of the writer, may safely be applied to the correspond- 
ing types of plant remains found to occur in the peat deposits of the 
Lake belt, e. g., Ohio (5) and the New England States, e. g., Massa- 
chusetts (7) , and present also in other States within the glaciated 
area of North America. For purposes of microscopic identification 
of plant remains the illustrations given in Friih and Schroter (10) 
afford an excellent basis for analysis and comparison. 
THE AQUATIC GROUP OF PEAT MATERIALS. 
Types of peat material (allochthonous) from open water and from 
shore stages of a vegetation series, of which the plant remains accu- 
mulated below the water level. 
The peat materials are structureless or coarsely macerated, soft, or 
compact and sticky, especially in older and deeper strata. They vary 
in composition, texture, color, etc., according to the depth of water 
and the character of the water in the initial stages of the area or of 
the vegetation series; they are largely, though not wholly, composed 
of the more resistant residues of plant remains, bits of woody and 
fibrous material, fragments of root and shoot tissue, the outer coats 
of cellular organisms, and a finely macerated debris as an embedding 
or binding ground mass which has either partly or wholly lost all 
vestige of its original organic structure. To this is added in various 
proportions and from various sources material of plant and animal 
origin, as well as dust, silt, etc., from the surrounding area, laid down 
by wind and current. 
Several distinct vegetation units which grow either free floating, 
wholly submerged, or rooted and partly submerged in water may 
form at any level considerable and extensive layers of material 
by the constant accretion of plant remains. These peat-forming 
plants are represented to-day by a great number of species and in- 
dividuals with semiaquatic habits of growth in fresh and brackish 
water. Among them are species of Ceratophyllum. Potamogeton, 
Castalia, Nymphaea, Peltandra, Pontederia, Polygonum, Decodon, 
