Page:The Journal of geology (IA journalofgeology21894univers).pdf/106

but are unable to ascend across the flood plain to the Mississippi; they therefore unite and form the Yazoo river which runs southward along the eastern margin of the flood plain, near the foot of the bluffs. It would have to pursue an independent course all the way to the Gulf, were it not that the Mississippi comes swinging across the plain, and picks up the Yazoo at Vicksburg.

But it is the topographical sheets of the U. S. Geological Survey that afford the greatest variety of illustrative material for this country; and it is not too much to say that the facts they present create a revolution in the student's knowledge of his home geography. We may well wish that they were more accurate, but, with all their imperfections, they present a great body of new information. Under the family of plains there are examples of low litoral plains in New Jersey and Florida, the latter being so young that the constructional lakes are not yet drained. The moderate advance in denudation of an upland—itself an old lowland of denudation—is seen in the meandering gorge of the Osage in central Missouri; the relatively uncut plateaus of Arizona are seen alongside of the beginning of their denudation in the grand canyon of the Colorado. Maturely dissected plateaus are found in West Virginia and eastern Kentucky; in northern Alabama and northern Arkansas; but the first two are of minute topographic texture; the second two are of coarser forms. Outliers of past-mature plateaus are shown on several sheets in central Texas. All manner of other illustrations are found in the same series of maps. The thoroughly adjusted streams of the Pennsylvania Appalachians; the superimposed streams of northern New Jersey; the Illinois river, the type of a medium-sized river in the abandoned channel of a large river; this being the only well-mapped example of the kind in this country; the warped intermontane valleys of Montana; Crater Lake in northern California; glacial lakes in Massachusetts; flood plains slanting away from their river in Louisiana; fiords in Connecticut; moraines in Rhode Island; drumlins in Wisconsin; trap ridges in New Jersey; revived old mountains in North Carolina; half-buried mountains in Utah and Nevada. Every