ABSTRACT
Skeletal soils are those that contain coarse fragments including gravels, stones, or rocks (Figs. 19.1 and 19.2). According to FAO (1977) classi-fication, the particles in a skeletal soil are classified based on size as gravel (2-75 mm), stones (75-250 mm), and boulders (>250mm). The Soil Survey Manual (Soil Survey Staff, 1951) classifies skeletal soils according to the diameter of round, subround, angular, or irregular fragments into gravel, pebbles, cobbles, stones, and boulders (Table 19.1a), as well as according to the length of flat fragments as channer, flagstone, stone, and boulder (Table 19.1a). The upper limit of sand content (2 mm) corresponds to the lower limit of coarse fragments. The pebbles, cobbles, and stones are all in the range from 76 mm to 250 mm. The Soil Survey Staff (1993) have classified the gravels in two major categories: (i) spherical, cubelike, or equiaxial, and (ii) flat (Table 19.1b).
