The straths are part of a mature, but ancient drainage system, which was graded a thousand feet above the level of the present streams and only a few hundred feet below the main upland. Certain broad depressions through the highlands east of the Connecticut Lowland suggest that this drainage pursued a southeastward course to the Atlantic, and that the river did not establish its modern course until the straths were elevated and notched. The land level above the strath-margins is a still older surface from which the rock-benches were cut. The higher surface stretches to the horizon at Pelham, but Mount Monadnock and Wachusett stand conspicuously above it. And on the Mohawk Trail one must ascend the tower at the eastern summit before any higher land comes into view. Greylock’s summit and the long chain of the Green Mountains attain greater elevations. The West River and Deerfield basins are graded to the level of this higher and older erosion surface, but farther north a chain of peaks including Stratton and Okemo swing eastward towards Ascutney. They appear to have formed a divide on this ancient land, as they do today; and beyond their crests rivers have run to the Saint Lawrence and Hudson basins from a time which antedated any of the familiar features of the New England landscape. Although this flat upland surface is more complex than it appears to the eye, it dominates all of southern New England, and ramifying arms of it penetrate northward into the White Mountains of New Hampshire and Maine. Another great arm passes west of Mount Greylock and spreads out between the Catskill Mountains and the Adirondacks. During the long period of erosion when it was formed, New England was reduced nearer to the grade of the main rivers than at any other time either before or since, and only rocks which have effectively resisted all later assaults by the geologic processes of destruction surmount the surface. To the eye, the region appears so nearly planed that it has been called the New England peneplane.