36 BULLETIN 802, U. S. DEPARTMENT OF AGRICULTURE. 



in barrier formation or, more likely, with the accumulation of 

 plant remains, and it practically maintained itself over the area of 

 active peat formation in close adjustment to the growth of the 

 plants holding back the natural drainage. Areas of that class of 

 peat deposits can be drained to the bottom and rarely need the 

 more elaborate drainage measures which aim to reduce the amount 

 of overflow in swamps and marshes resulting from river inunda- 

 tion. 



Attention needs to be called to the fact that the dominant timber 

 component alone is not always significant of the capabilities of these 

 types of peat material. The plant remains derived from evergreen 

 shrubs, such as the azalea and rhododendron, or from deciduous 

 undergrowth in forests may alter the value of the material con- 

 siderably. This is well illustrated in the distinction made by some 

 authors between the " mild humus " characteristic of deciduous for- 

 ests, well aerated and containing beneficial soil organisms, and the 

 " raw humus " found in coniferous forests in which decay-producing 

 organisms are usually less abundant. 



ALDER-WILLOW TYPE. 



" Alnus-Salix peat," " Brucliwaldtorf." 



BIRCH TYPE. 



" Betula peat," " tjbergaiigswaldtorf." 



Brown to chocolate-brown peat material, wickerlike in appear- 

 ance on account of the numerous small twigs and branches of alder 

 {Alnus spp.), willow {Salix spp.), and other species of deciduous 

 shrubs which form a considerable portion in the fibrous or frag- 

 mental plant remains. The woody components often consist of 

 bark and other recognizable, slowly disintegrating parts from birch 

 {Betula spp.), but with the exception of the resinous components the 

 material is- as a rule relatively soft, easily cut, and tends to become 

 brittle and granular when dry, breaking down into a blackish 

 coarsely grained debris. Material which is well disintegrated or 

 contains a large proportion of plastic ground mass takes on a com- 

 pact structure and often resembles a hard substance when dry. 



The plant remains are derived from shrubs, among which the 

 alders, buttonbushes, and willows are the most common. Birch and 

 ericaceous heath shrubs appear to be more numerous in individuals 

 on peat deposits of the Northern States and in European countries. 



The analyses presented in Tables I and II are intended to point out 

 some of the features of practical value to agriculture and to tech- 

 nical interests. 



DECIDXJOUS-FOREST TYPES. 

 " Laubwaldtorf." 



Loose, mingled debris of partly decayed branches, twigs, bark, and 

 other aerial parts of plants falling to the ground and becoming in- 



