Interparticle friction is the principal property which permits soils and granular materials to resist load without formation. Dry soils of virtually all types are highly stable. The suitability of soils for engineering purposes depends largely upon their ability to remain in place and support whatever loads may be placed upon them, either by a permanent engineering structure or by transient vehicle loads. A study of the properties which distinguish the more satisfactory from the less satisfactory soils indicates that in the majority of eases clays are detrimental to stability. It is apparent that wet clay has the effect of a lubricant in diminishing the natural resistance due to friction that would otherwise exist. It is necessary that the civil engineer responsible for construction of any form of earth work should be informed not only concerning the Quantity of clay minerals that are present but also about their nature and their potential influence on the engineering properties of the soil.