PLANT TISSUE _________________ | _Residual Products_ | _Evolved Products_ | Peat. } | } Lignite. } | } { Carbonic Acid. Bitumious Coal. } { Carbonic Oxide. | } { Carbureted Hydrogen, etc. Semi-bitumious " } { Water. | } { {Maltha. Anthracite. } { { | | } { {Asphalt etc. 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 more homogeneous and darker until at the bottom of the marsh ten or twenty feet from the surface, we have a black, carbonaceous paste, which, when dried, resembles some varieties of coal, and approaches them in composition. It has lost half the substance of the original plant, and shows a marked increase in the relative proportion of carbon.