The humid tropics: weathering and laterites
519
Figure 20.13. Deep weathering distribution in metres, in a fine-grained, biotite granite, near Jos, northern
Nigeria. 1 Outcrops of unweathered granite showing contours at 15 m intervals. On the cross sections
(A-B, C-D) saprolite is ruled (after Thomas (1966), in Thomas (1994), Figure 3.16).
Obviously, the zonation of weathering profiles on sedimentary, metamorphic and
volcanic rocks is very variable, although the Ollier profile type is also applicable. In all
of them rock fissuration plays a fundamental role. Other profile divisions can be made
based upon chemical, mineralogical, hydrological, or engineering criteria, depending on
the objectives (Ollier, 1984).
519
Figure 20.13. Deep weathering distribution in metres, in a fine-grained, biotite granite, near Jos, northern
Nigeria. 1 Outcrops of unweathered granite showing contours at 15 m intervals. On the cross sections
(A-B, C-D) saprolite is ruled (after Thomas (1966), in Thomas (1994), Figure 3.16).
Obviously, the zonation of weathering profiles on sedimentary, metamorphic and
volcanic rocks is very variable, although the Ollier profile type is also applicable. In all
of them rock fissuration plays a fundamental role. Other profile divisions can be made
based upon chemical, mineralogical, hydrological, or engineering criteria, depending on
the objectives (Ollier, 1984).