Graphitie Anthracite. } { Petro- { |
| } { leum {Asphaltic Coal.
Graphite. } { |
| } {Asphaltic Anthracite.
Ash. } { |
{ " Graphite.

[NOTE.--In this diagram, the vertical line connecting the names of the
residual products (and of the derivatives of petroleum) indicates that
each succeeding one is produced by further alteration from that which
precedes it, and not independently. Also, the arrangement of the braces
is designed to show that any or all of the evolved products are given
off at each stage of alteration.]

The theory here proposed has not been evolved from my inner
consciousness, but has grown from careful study, through many years, of
facts in the field. A brief sketch of the evidence in favor of it is all
that we have space for here.


RESIDUAL PRODUCTS.

_Peat_.--Dry plant-tissue consists of about 50 per cent, of carbon,
44 per cent, of oxygen, with a little nitrogen, and 6 per cent. of
hydrogen. In a peat-bog, we find the upper part of the scale represented
above very well shown: plants are growing on the surface with the normal
composition of cellulose. The first stratum of peat consists of browned
and partially decomposed plant-tissue, which is found to have lost
perhaps 20 per cent. of the components of wood, and to have acquired an
increasing percentage of carbon. As we descend in the peat, it becomes