REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1901 r57 



but may also spread toward the center of the lake, forming a 

 mass of floating vegetation. This growth often covers event- 

 ually the whole sheet of water, but at the same time thickens, 

 for, as the plants die off in any one place, new ones spring up 

 on their remains. In this way the pond often becomes entirely 

 filled with a spongy mass of matted plant fragments. Such a 

 deposit is known as peat^ and a section made through a peat 

 bog from top to bottom will show a layer of living plants at the 

 surface, which grow on the clearly outlined stems and roots of 

 dead ones, while below these is a gradual passage into fully 

 formed peat, in which little trace of the original vegetable 

 fibers may be discernible. This lower part is the peat proper, 

 though the name is often broadly used to include the overlying 

 layers. 



Peat is very spongy in its character and varies in color 

 from brown to black. It may also show variation in structure, 

 some peat being very fibrous, while other varieties show little 

 fibrous character and are rather cheesy when moist. 



The process of peat formation is not one of complete decay s 

 but one of slow oxidation which takes place away from contact 

 with the air. In this change hydrogen, nitrogen and some 

 oxygen pass off, indeed the formation of peat is entirely similar 

 to the first stages in the formation of coal. 



As the deposit gains in depth the decomposition of the vege- 

 table matter continues, and this is accompanied by the evolution 

 of gases and a densification of the mass. 



This change of vegetable matter into peat is quite different 

 from that taking place when the same material decays under 

 the soil in drained land. The decayed vegetable matter or 

 humus formed under these latter conditions is much darker, 

 sometimes even black, 1 and is insoluble in water, to which it 

 imparts no brown color, while the humus of bog peat is soluble. 

 This insoluble humus is the form most desired by the farmer. 

 The brown humus of bogs can however be rendered insoluble by 

 lime. 



'Hilgard, E. W. Cal. Exp. Sta. 1892-93. p. 11. 



