Load casts are bulges, lumps, and lobes that can form on the bedding planes that separate the layers of sedimentary rocks. The lumps "hang down" from the upper layer into the lower layer, and typically form with fairly equal spacing. These features form during soft-sediment deformation shortly after sediment burial, before the sediments lithify. They can be created when a denser layer of sediment is deposited on top of a less-dense sediment. This arrangement is gravitationally unstable, which encourages formation of a Rayleigh-Taylor instability if the sediment becomes liquefied (for instance, by an imposed earthquake shock). Once the sediments can flow, the instability creates the "hanging" lobes and knobs of the load casts as plumes of the denser sediment descend into the less-dense layer. Load casts are a common kind of sole marking. Terminology The expression "load cast", sometimes also called a load structure, refers to a load (the denser layer) sinking into its underlying (less dense) cast (mold). Related to load casts are flame structures, load waves, and anticrests. Extreme developments of load casts are pseudo-nodules and ball-and-pillow structures. In these extreme cases, the hanging lobe becomes almost or completely detached from the overlying bed, resulting in apparently isolated masses of the overlying material floating in the lower bed. History Load casts were scientifically reported for the first time by the sedimentologist Theodor Fuchs in 1895 who called them in German Fließwülste (flow crests, flow warts). He also reproduced the structure experimentally. Later studies were conducted by Henry Clifton Sorby in 1908, Paul Kukuk in 1920, and by Robert Shrock in 1948. Description Load casts form on the underside of the overlying denser layer (sands, coarse sands, or gravels), which is superimposed on a less-dense hydroplastic layer (muds, silts or finer sands). The casts take on the form of slight bulges, swellings, deep or rounded sacks, knobby excrescences or highly irregular protuberances. In profile, they appear as a row of flattened, lobe-shaped masses of similar size, shape, and spacing bulging into the lower layer. Between the lobes penetrate flame-like fingers or diapir-like shapes from the underlying less-dense layer. In 3-D, the lobes reveal equant to elongated pillow shapes separated from each other by narrow clefts. In profile, the succession of lobes and fingers can be modelled as a row of semi-circular lobes touching each other at the finger tips; a characteristic wavelength L can consequently be attributed to the