bar finger

Bar fingers are elongated lenses of sand or sediment lying beneath the distributary channels of bird-foot river deltas. As Andrew Goudie explains in The Nature of the Environment: “If a river branches where it enters the sea to form distributaries, the distributaries will build outwards as long sand fingers, called bar-finger sands; whereas the finer muds and silts get washed into the still water between the distributaries, so that they gradually fill up with mud and swamp deposits.” Such a delta takes the shape of a heron’s foot—narrow, splayed toes, each consisting of a river channel banked on either side by marshland. The underlying bar fingers enjoy other anatomical associations as well. A bar finger can be lingulate (tongue-shaped), and their sands are often characterized as being coarser upstream at the “bar head” and finer downstream at the “bar tail.”

Mike Tidwell