“O) 
$< 
i- 
‘d 
e 
1 
d 
2 
{. 
COAL AND ITS CLASSIFICATION 261 
ture—and by change into a more compact, heavier, and 
more brittle substance. 
Humic Series. 
—— 
0 
Wood . , 
Peat . . . 
Lignite . . 
Bituminous coal . . 
Steam v ' 
Anthracite (Pennsylvanian) 
[00 
100 
100 | 
100 
100 
. 
[2°2 83 
9:6 557 
75 6o 
6:6 93 
45 | 26 
2:8 1 
Sapropelic, 
oy 
Wigan Cannel 
LOO 
59 
10°11 
Pear—Peat represents the first stage in one method of coal 
formation. It is soft, brown or black, and varies in texture 
from a fibrous material in which the plants can be recognized 
to structureless jelly. It is an accumulation of vegetation 
due to the simultaneous growth and decay of plants when 
saturated with water, which prevents their complete decom- 
position into water and carbon dioxide. The plants at the 
upper part of the deposit decay under the action of the oxygen 
of the air and of bacteria and fungi; but in the lower layers, 
as air is excluded and the conditions are aseptic, chemical 
decomposition is prevented, and the materials accumulate 
by the continued growth of the plants above. The name 
probably comes from a Celtic word meaning pieces, as peat 
can be pulled into shreds of vegetation; it was known in 
England as turf until the name peat spread from Scotland 
late in the eighteenth century. 
Peat is usually formed on cold moorlands by the growth of 
mosses and rushes. It is most abundant between 35° and 
60° N. where the mean annual temperature is from 40° to 
60° F. Its close dependence on this temperature probably 
explains why its formation has ceased on some Scottish moor- 
lands, though in Ireland and Germany it grows at the rate of 
a foot in from 5 to 10 years. Peat is comparatively rare in 
warmer countries, where plant decay is usually complete ; 
it occurs in Italy, East Africa, Madagascar, and such places