Total gallium content in soils is anticipated to be linked closely with underlying parent material, as deposition or addition levels will have been low and parent material mineralogy is a strong controlling factor of gallium content (Mielke, 1979). As such, the presence of a strong predictive accuracy for gallium indicates a strong relationship between parent material and soil colour, which is not surprising. An obvious question is there fore why other elements such as vanadium and chromium, the soil contents of which are also related to parentmaterial, are not predicted as accurately. One possible reason for this is that gallium has no biological roles and very few roles in industry (i.e. microelectronics), while elements such as vanadiumand chromium are eithermore biologically active or have awider range of uses and therefore potential pollutive sources within industry.