According to Atterberg's definition a clay can be considered to be in a plastic state, if its water content ranges between the lower and the upper limit of the plastic state. Although, by necessity, the methods for determining the limits are somewhat arbitrary, Atterberg's range of plasticity includes clay‐water mixtures which have a fairly well‐defined group of properties in common. Within this range an appreciable force is required to produce a continuous, plastic flow of the material and under the influence of forces beneath the “yield point” the material exhibits all of the characteristic elastic properties of imperfectly elastic solid bodies.