The Parish of Orleans, located near the southeastern extremity of the Mississippi Alluvial Plain, lies wholly within the delta. With the exception of a few minor outcrops of sea-island sand and lake-shore deposits of sand and clam shell, all surface formations within the parish are alluvial. The major topographic features are the natural levees along the Mississippi and Gentilly ridges and along Bayou Sauvage, a former outlet of the river.
The higher parts of these ridges, or 'frontlands,' are composed of sandy loams. These dip and graduate into the 'backlands,' where the soil is composed of a lighter loam and waxy clay. Deposits of stiff, blue clay fill the area between the ridges, except near the lake shores and passes, where the alluvial material has been reworked by tidal action. Here the soil consists of mucky masses of partly decomposed vegetation interspersed with a fine, drab-colored clay. Fine peat soil formed by marsh vegetation in a state of partial decay sometimes accumulates over extensive low areas to a depth of from one to three feet on the surface of the blue clay.
Fossils consist mainly of marine shells and oysters associated with seashore deposits, and clam shell (Rangia cuneata) associated with the clay deposits. Indian relics are numerous on the shell ridges near the lakes, and broken bits of pottery can be found mixed with oyster and clam-shell fossils along the lake beaches. Iron concretions and fossil cypress wood are found in the blue clay.