Sole markings
Sole marks are sedimentary structures found on the bases of certain strata, that indicate small-scale (usually on the order of centimetres) grooves or irregularities. This usually occurs at the interface of two differing lithologies and/or grain sizes. They are commonly preserved as casts of these indents on the bottom of the overlying bed (like flute casts). This is similar to casts and molds in fossil preservation. Occurring as they do only at the bottom of beds, and their distinctive shapes, they can make useful way up structures and paleocurrent indicators. Sole markings are found most commonly in  turbidite deposits, but are also often seen in modern river beds and tidal channels. History. Sole markings were first recognized in the Devonian rocks of New York State by James Hall in 1843. Originally, the features found on the undersides of beds were called "hieroglyphs", "fucoids", and "bio hieroglyphs", because of their structure and how they were thought to be created; however, the term "sole mark" is used by geologists at present. Scour marks and flute casts. Scour marks and flute casts are scours dug into soft, fine sediment which typically get filled by an overlying bed (hence the name  cast). Measuring the long axis of the flute cast gives the direction of flow, with the tapered end pointing toward the flow and the steep end up current. The concavity of the flute cast also points stratigraphically up. Flute casts can be characterized into four types, parabolic, spindle-shaped, comet-shaped, and asymmetrical. Tool marks. Tool marks are a type of sole marking formed by grooves left in a bed by things like sticks being dragged along by a current. The average direction of these can be assumed to be the flow direction, though it is bidirectional, so it could  be either way along the mark. Tool marks also have a more specific breakdown. There are grooves and striations, skip or prod marks, and roll marks. Groove or striation marks result from the continuous contact with the muddy bed. Skip or prod marks come from objects that bounce along the surface of the muddy bed. And roll marks result from objects rolling along the muddy bed. Groove casts. Groove casts are straight parallel ridges that are raised a few millimeters from the bedding surface. These structures were named and defined by Shrock in 1948 because of their long and narrow  appearance, and they were formed from the filling in of grooves. Even though they may seem similar to flute casts, they each have many distinguishing characteristics, and the two are generally not found in the same vicinity. Groove casts are closely spaced, but not on top of each other, and exist in pairs, triples, and even larger groups. Groove casts form when high velocity flows (e.g. turbidite) create a pattern on an underlying bed. In 1957, Kuenen published that "groove cast" was a general term encompassing both drag marks and slide marks. Load casts. Load casts are secondary structures that  are preserved as bulbous depressions on the base of a bed. They form as dense, overlying sediment (usually sand) settles into less dense, water-saturated sediment (usually mud) below.