But this sliding scale of solid compounds, which we designate by
the names given above, is not the only product of the natural and
spontaneous distillation of plant tissue. Part of the original organic
mass remains, though constantly wasting, to represent it; another part
escapes, either completely oxidized as carbonic acid and water, or in
a volatile or liquid form, still retaining its organic character, and
destined to future oxidation, known as carbureted hydrogen, olefiant
gas, petroleum, etc.

Hence, in the decomposition of vegetable tissue, two classes of
resultant compounds are formed, one residual and the other evolved; and
the genesis and relation of the carbon minerals may be accurately shown
by the following diagram:

PLANT TISSUE
_________________
|
_Residual Products_ | _Evolved Products_
|
Peat. }
| }
Lignite. }
| } { Carbonic Acid.
Bitumious Coal. } { Carbonic Oxide.
| } { Carbureted Hydrogen, etc.
Semi-bitumious " } { Water.
| } { {Maltha.
Anthracite. } { { |
| } { {Asphalt etc.