white: eelations between coal and petroleum 191 



microbian action has progressed further the coal-forming sub- 

 stance consists more fully of the products of the biochemical 

 decomposition of the vegetal matter, in which the surviving, 

 often comminuted, structural fragments, consisting of the tis- 

 sues and plant products most resistant to the agencies of sub- 

 aqueous decay, are embedded. Coals originating in mature or 

 much decomposed peats and containing little coarse detritus 

 are sometimes called '^amorphous," although they are never 

 without vestiges of plant structures. 



In many cases the decay of great amounts of resin-bearing 

 gymnospermous wood has, through the disintegration of the 

 woody tissue, set free and effected a concentration of large quan- 

 tities of resinous matter which was resistant to the decomposing 

 agents in the peat swamps or bogs. Also, under certain con- 

 ditions of deposition, especially where the water was too deep 

 for the growth of subaerial types of vegetation, and stagnant 

 or nearly so, the organic mass may have been largely or almost 

 wholly made up of the spore and pollen exines and grains of 

 resin, mingled in varying proportions with aquatic plant and 

 animal life of low orders, some of which is plankton. The latter 

 may include the remains of innumerable algae, with protozoans, 

 small Crustacea, insect eggs and larvae, small gastropods, etc., 

 and even fish. More or less spore, pollen, and resin ingredients 

 enter into the xyloid and other coals of the ordinary types; but 

 whenever they become conspicuous in the composition of the 

 coal, they impart a so-called ''fatty" quality to it; and when 

 they form the greater part of it, being generally mingled with 

 increased amounts of plankton material, as is natural in an open 

 water habitat, they form cannels. 



Between coals of the ordinary, or humic, types and the cannels 

 there is complete intergradation. Locally, according to the cir- 

 cumstances of deposition, the Paleozoic cannel coals contain 

 peculiar forms of organic remains that have, by most paleo- 

 botanists, been regarded as algae of very low groups.^ If the 

 so-called algae and other plankton remains predominate, com- 

 posing the greater part of the organic deposit, the latter is called 



'Renault, B., Microorganismes des combustibles fossiles, p. 151. 1893. 



