ABSTRACT
The strength of rock, or of less well consolidated sediment, is influenced by the mineralogy of its particles and by the character of the particle contacts. Burial and uplift are frequently recurring aspects of geological history. During burial the volume of sediment is reduced because water is squeezed from its pores. The deformation of rock at very slow rates of strain involves processes collectively described as creep. Rock behaves as an elastic material when loaded rapidly and recovers its strain when unloaded, hence elastic deformation is a part of rock behaviour. The overburden load is progressively reduced above rocks as they are raised towards ground level and this permits them to expand in the vertical direction. The geological loads under which the clay has consolidated have produced a small amount of visco-elastic deformation and the lateral stresses within the sediment cannot be calculated accurately from knowledge of vertical stress and the theory of elasticity.
