5oo 



HISTORICAL GEOLOGY 



places, although evidence has been advanced recently which shows 

 that much coal was formed from organic matter, spores, wood, and 

 leaves, carried into swamps and lakes. It is a matter of common ob- 

 servation that wood decays much less rapidly below water than above 

 it. This is shown by piles and posts which may be entirely rotted 

 away where exposed to the air, while they are well preserved where 

 continually soaked with water. The reason is to be found in the 

 fact that vegetation in the open air is readily attacked by destroying 

 fungi, the carbon is oxidized to carbon dioxide and the hydrogen to 

 water, and as these are volatile the entire substance of the plant may 

 disappear; while in water the oxidation proceeds much less rapidly 

 and completely, and wood-destroying organisms cannot flourish in 

 water. Of the vegetation of luxuriant forests only thin layers of 

 humus remain, and the abundant vegetation of dry, fertile plains fails 

 to accumulate, although the slow-growing bog moss (sphagnum) of 

 cold regions may accumulate to form thick beds of peat. 1 



(2) How it was Kept from Decay. — The chemical changes which 

 take place in vegetable tissue (which has a composition approximately 

 of C 6 HioO B ) when deposited in water, result in the formation of marsh 

 gas (CH4), carbon dioxide (C0 2 ), and other gases. The effect of 

 these changes consists in (1) a reduction in volume, (2) a reduction 

 in the volatile constituents, (3) a reduction in the amount of water, 

 and (4) a relative increase in the percentage of carbon, since although 

 the greater part of the hydrogen and oxygen are removed, the carbon 

 is only moderately reduced. 



The proof in support of the assumption that the great coal deposits 

 were developed in swamps, the vegetation accumulating where it 



1 " The peat-bog hypothesis, or growth in situ (autocthonous) hypothesis, at the present 

 moment has won the adhesion of the majority of the geologists, although it encounters the serious 

 difficulty that peat bogs are not found in the parts of the earth which at the present time 

 present the nearest approach to the conditions of climate obtaining in the great coal-forming 

 epochs. The lacustrine or transport hypothesis, which is better applicable to the conditions 

 of warmth which are generally conceded to have existed in the most active periods of coal 

 formation, has had few adherents in recent years outside of France. It is, however, the 

 hypothesis which harmonizes best with the structures found in coals as the result of micro- 

 scopic examination. The bottom of every lake is filled with countless pollen grains or 

 spores. As the bottom becomes shallower, water lilies and other water plants make their 

 appearance and add their remains to the lacustrine accumulations. Finally the coarser 

 debris of the land plants is added to the heap and not long afterwards mosses, grasses, 

 sedges, heaths, and ultimately forest trees, may flourish, where once was open water." 

 Jeffrey, E. C, — On the Composition and Qualities of Coal: Economic Geology, Vol. 9, 

 191 I. PP. 7.50 742. 



It i believed by this investigator that practically all coal is floated material and has not 

 originated from plant remains in situ, and microscopic evidence is stated by him to place this 

 beyond question. 



