PROPERTIES AND USES OF CELL WALLS 105 



The 30 ft peat layer of the Sumatra Swamp covers an area of 

 about 300 square miles, and would yield a 3 ft coal deposit. 



The rate of peat accumulation varies widely according to type 

 of vegetation, its growth rate, the soil, climate, and rate of decay. 



In the Jura Mountains, 18-20 in. of peat have accumulated 

 in 50 years. In the valley of the Somme, 1 in. per year accumulates 

 and in moss areas of Denmark, 250-300 years are required for 

 laying down of 10 ft. Under the most favorable conditions, a rate 

 of 2 in. per year is possible. Old, compressed peat represents one- 

 -eighth the thickness of fresh deposits, hence accumulates at the rate 

 of about 0.1 in. per year. In general 20 ft of vegetable debris or 

 3 ft of old peat correspond to 1 ft of bituminous coal. The trans- 

 formation of vegetable debris or fresh peat into 1 ft of bituminous 

 coal is estimated to require 300 years. 



Although they must be regarded as highly empirical expressions, 

 a number of overall equations for coal formation have been pro- 

 posed on the basis of the conversion of cellulose. For example, 

 the formation of bituminous coal from the wood of Cordaites 

 has been written: 



(C 6 H 10 O 5 )4^C 9 H 6 O+7CH4+8CO 2 +3H 2 O 



The value of such gross equations is highly questionable. 



Tn the transformation of vegetable matter into coal it is possible 

 to recognize two stages-the biochemical-fermentative, and the 

 geophysical-geochemical. In the stage I, soil bacteria in conjunc- 

 tion with autolytic processes macerate plant tissues, release or 

 solubilize many constituents, and degrade or modify many of the 

 chemical components thus made available. Bacteria are known 

 in peat and coal, Micrococcus and Streptococcus, for example, 

 and some forms are known to operate at depths of at least 25-30 ft 

 in peat bogs. The level of bacterial activity must eventually become 

 restricted to anaerobes and will eventually be checked by C0 2 

 and organic acids which lower the pH. 



The principle events which have been definitely associated with 

 the biochemical stage in coalification are the disaggregation of 

 tissues and selective degradation of carbohydrates and other 

 primary cellular components. The more resistant secondary sub- 



