delta

A name given by the Greeks to the alluvial tract inclosed between the bifurcating branches of the Nile and the sea-line. It is well known that rivers which deposit great quantities of matter, do also very often separate into two or more branches, previous to their discharge into the sea; thus forming triangular spaces, aptly called deltas from their resemblance to the Greek letter Δ.

All deltas appear by their section to be formed of matter totally different from that of the adjacent country. They are the creation of the rivers themselves, which, having brought down with their floods vast quantities of mud and sand from the upper lands, deposit them in the lowest place, the sea; at whose margin, the current which has hitherto impelled them ceasing, they are deposited by the mere action of gravity. This is particularly illustrated on the western coast of Africa by the shoals off the Rio Grande, Rio Nunez, and others. The coast, as well as the embouchures of the rivers, exhibit a deposit of deep mud, and yet far at sea banks of clean siliceous sand arise.