45 



soil 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 

 contact, provided the thickness of the organic soil 

 materials is more than twice that of the mineral soil 

 above the contact; or 



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

 mental material (gravel, stones, cobbles) and the inter- 

 stices are filled with organic materials, or rests on a 

 lithic or paralithic 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 arti- 

 ficially 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 frag- 

 mental material having interstices filled with organic 

 materials. 



Soils that do not satisfy the criteria for classification 

 as organic soils are mineral soils. 



