The angle at which granular material comes to rest, varying inversely with fragment size in perfectly sorted materials, but directly in those imperfectly sorted; inversely with fragment density; directly with fragment angularity, roughness, and compaction; inversely with height of fall of material on free cones; and directly with moisture content up to saturation point, but inversely thereafter (van Burkalow (1945) GSA Bull. 56, 6).