Delta
the name of the fourth Greek letter, corresponding with the English d. As a capital tal it is formed in the shape applied to the triangle-shaped island of an equilateral triangle. Originally formed by deposits between the two mouths of the Nile; afterward applied to other similarly shaped tracts formed at the mouths of large rivers by two or more diverging branches. The deltas of many rivers, as the Ganges, Niger, Mississippi, etc., are geologically most instructive, exhibiting, as they do, perfect analogues of many of the older formations in magnitude, variety of composition, alternation of beds, and entombment of plants and animals.