The boundary between the prairie and Ozark regions follows the Missouri river from its mouth to Glasgow, running thence south-westward, with irregular limits, but with a direct trend, to Jasper county at the south-east corner of Kansas; and the boundary between the Ozark and embayment regions runs due south-west from Cape Girardeau.
The head of the coastal plain embayment is near the junction of the Ohio and the Mississippi.
The Mississippi embayment is in parts predominantly sandy, in others clayey; it is mainly under timber.
Ash, oaks, black and sweet gums, chestnuts, hickories, hard maple, beech, walnut and short-leaf pine are noteworthy among the trees of the Carolinian area; the tupelo and bald cypress of the embayment region, and long-leaf and loblolly pines, pecans and live oaks of the uplands, among those characteristic of the Austro-riparian.
The embayment region is of 'Tertiary origin, containing deposits of both neocene and eocene periods.
The special features of the Gulf Plain are the peninsular extension of the plain in Florida, the belted arrangement of relief and soils in Alabama and in Texas, and the Mississippi embayment or inland extension of the plain half-way up the course of the Mississippi river, with the Mississippi flood plain there included.
After constriction from the Mississippi embayment to 250 m.
The most striking feature of the embayment is the broad valley which the Mississippi has eroded across it.
The south-eastern embayment is rich to an exceptional degree.
The entire state is included within the Austro-riparian life zone; the higher portions fall within the Carolinian area and the lower portions, including the Gulf and the Mississippi embayment almost to the N.E.