shallow lakes (Lake Pontchartrain on the east, and Grand Lake on the west of the river). The ordinary triangular form of deltas, due to the smoothing of the delta front by sea action, is here wanting, because of the weakness of sea action in comparison with the strength of the current in each of the four distributaries or passes into which the river divides near its mouth. Coastal plain in Louisiana and Texas After constriction from the Mississippi embayment to in western Louisiana, the coastal plain continues southwestward with this breadth until it narrows to about in southern Texas near the crossing of the Colorado River (Texas Colorado River, not the Colorado River that flows through the Grand Canyon), but it again widens to at the national boundary as a joint effect of embayment up the valley of the Rio Grande and of the seaward advance of this river's rounded delta front. These several changes take place in a distance of about . It includes a region of over , less than half of the large state of Texas. A belted arrangement of reliefs and soils, resulting from differential erosion on strata of unlike composition and resistance, characterizes almost the entire area of the coastal plain. Most of the plain is treeless prairie, but the sandier belts are forested. Two of them are known as cross timbers, because their trend is transverse to the general course of the main consequent rivers. An inland extension from the coastal plain in north-central Texas leads to a large escarpment known as Grand Prairie (not structurally included in the coastal plain), upheld at altitudes of 1,200 or by a resistant Cretaceous limestone. This dips gently seaward with its scalloped inland-facing escarpment overlooking a denuded central prairie region of irregular structure and form. Its gentle coastward slope of per mile (3 m/km) is dissected by many branching consequent streams. In its southernpart as it approaches the Colorado river, the escarpment is dissected into a belt of discontinuous hills. The western cross timbers follow a sandy belt along the inner base of the ragged escarpment of Grand Prairie. The eastern cross timbers follow another sandy belt in the lowland between the eastern slope of Grand Prairie and the pale western escarpment of the immediately eastward and lower Black Prairie escarpment. This escarpment is supported at an altitude of or less by a chalk formation, which gives