Formation Processes



 The term "stone line" was originally proposed by Sharpe (1938) to

designate "a line of angular to subangular fragments which parallels a

sloping surface to a depth of several feet." Ruhe (1959, p. 223),

summarizing the definitions of several studies (Sharpe, 1938; De

Heinzelin, 1955; Parizek and Woodruff, 1957), defined a stone line as "a

concentration of coarser rock fragments in soils; in cross section it

may be a line, one stone thick or more than one stone in thickness, that

generally overlies material weathered in place from bedrock and that

usually is overlain by variable thicknesses of finer-textured sediment."

De Heinzelin (1955) objected to the term when used to designate the

gravel horizons common to equatorial African soils. He proposed instead

the term "nappe de gravat" (sheet of gravel), because it more

appropriately described the three-dimensional nature of the structure.

However, at present the term stone line is widely used in both the

English and French pedological literature.

 The formation processes that create stone lines instill specific

 morphological characteristics to the soil profile. It is these

 morphological characteristics that have been used to develop hypotheses

 concerning the formation processes. Pedologists working throughout

 equatorial Africa on a variety of landscapes have developed two

 different schools of thought concerning stone-line formation. These

 were categorized as either autochthonous (same) or allochthonous

 (different) with respect to the parent material of the stones and of the

 underlying material (Collinet, 1969). The distinction between the two