43 



materials accumulate in or under water. Leaf litter may rest 

 on a lithic contact and support a forest. The only soil in this 

 situation is organic in the sense that the mineral fraction is 

 appreciably less than half the weight and is only a small 

 percentage of the volume of the soil. 



DEFINITION OF ORGANIC SOILS 

 Organic soils (Histosols) are soils that 



1. Have organic soil materials that extend from the surface 

 to one of the following: 



a. A depth within 10 cm or less of a lithic or paralithic con- 

 tact, provided the thickness of the organic soil materials 

 is more than twice that of the mineral soil above the con- 

 tact; or 



b. Any depth if the organic soil material rests on frag- 

 mental material (gravel, stones, cobbles) and the interstices 

 are filled with organic materials, or rests on a lithic or para- 

 lithic contact; or 



2. Have organic materials that have an upper boundary 

 within 40 cm of the surface and 



a. Have one of the following thicknesses: 

 (1) 60 cm or more if three-fourths or more of the volume 



is moss fibers or the moist bulk density is <0.1 g per cubic 

 centimeter (6.25 lbs per cubic foot); 

 (2) 40 cm or more if 



(a) The organic soil material is saturated with water 

 for long periods (>6 months) or is artificially drained; 

 and 



(b) The organic material consists of sapric or hemic 

 materials or consists of fibric materials that are less 

 than three-fourths moss fibers by volume and have a 

 moist bulk density of 0.1 or more; and 



b. Have organic soil materials that 



(1) Do not have a mineral layer as much as 40 cm thick 

 either at the surface or whose upper boundary is within 

 a depth of 40 cm from the surface; and 



(2) Do not have mineral layers, taken cumulatively, as 

 thick as 40 cm within the upper 80 cm. 



It is a general rule that a soil is classed as an organic 

 soil (Histosol) either if more than half of the upper 80 cm 

 (32 in.) [sic] of soil is organic or if organic soil material of 

 any thickness rests on rock or on fragmental material 

 having interstices filled with organic materials. 

 Soils that do not satisfy the criteria for classification as 

 organic soils are mineral soils. 



