The occurrence of the lake basins in the lowland belts on either side of the Niagara cuesta is an abnormal feature, not to be explained by ordinary erosion, which can produce only valleys.
The discovery of this significant looped arrangement of the morainic belts is the greatest advance in interpretation of glacial phenomena since the first suggestion of a glacial period; it is also the strongest proof that the ice here concerned was a continuous sheet of creeping land ice, and not a discontinuous series of floating icebergs, as had been supposed.
Thus local sheets or aprons of gravel and sand are spread more or less abundantly along the outer side of the morainic belts; and long trains of gravel and sands clog the valleys that lead southward from the glaciated to the non-glaciated area.
In the embayment of the coastal plain some low cuesta-like belts of hills with associated strips of lowlands suggest the features of a beltedcoastal plain; the hillybeltordissected cuesta determined by the Grand Gulf formation in western Mississippi is the most distinct.
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.