SOIL AND SUBSOIL. 



127 



PROGRESS OF HUMIFICATION, AND FORMATION OF COAL. 

 (MOISTURE AND ASH OMITTED FROM CALCULATIONS.) 



The steady increase of carbon and nitrogen, together with 

 a corresponding decrease of oxygen, are well illustrated in the 

 analyses, especially in the strictly comparable series of peat 

 samples from various depths. In this case there is also a steady 

 decrease of hydrogen, and an increase of ash from 2.72% in 

 the surface layer, to 9.16 at 80 inches depth. This increase is 

 due in the main, of course, to the progressive volatilization of 

 the organic matter in the forms of carbonic dioxid and marsh 

 gas (methan, CH 4 ). 



In considering this table it should not be forgotten that 

 while normal humus stands very close to peat, and the latter 

 when compressed in certain stages would be undistinguishable 

 from lignite or brown coal; yet both peat and lignite are 

 known to be formed under conditions permitting much less 

 access of air or oxygen than occurs in the formation of normal 

 black soil-humus. Hence even black peat cannot at once stand 

 in place of soil-humus when removed from its watery bed, but 

 requires considerable time and aeration (oxidation), and in 

 most cases neutralization with lime or marl, before it can serve 

 the purposes of humus in the soil. 



Lignite and the progressively more carbonaceous coals are and have 

 been formed under the conjoined action of submergence and pressure, 

 sometimes also aided by heat ; and thus they cannot perform the func- 

 tion of soil-humus, any more than the fire-clays or shales underlying 



1 Detmer, Landw. Versuchst, Vol. 14, 1871. 



