ABSTRACT
The materials in which sub-aerially formed hillslopes are cut range from hard crystalline rocks to loose friable sands. In most environments there is also a layer of soil and/or regolith forming the uppermost portion of the underlying material. The thickness of this layer varies so that the surface form of a hillslope reflects both the shape of the mass of underlying rock or sediment and the local thickness of the soil/regolith layer. Through their physical, chemical and structural properties these materials affect hillslope processes and thereby influence hillslope form. In examining this influence it is convenient to consider materials in three groups: rocks, unconsolidated deposits and soils. The boundaries of these three groups are imprecise. For the purposes of this chapter, materials are termed rocks if they have undergone diagenic processes or otherwise possess structural features (joints, bedding planes etc.) that may influence their effect on hillslope form. The section on unconsolidated materials is concerned primarily with accumulations of loose rock fragments, but also examines cohesive deposits. The discussion of the influence of soils is concerned wholly with the effects of the surface layer which is taken to include both the weathered material that is undergoing pedogenic processes and the vegetation.
