After the upraised peneplain from which the long, even-crested ridges of the Appalachians were produced by the excavation of the bordering valleys had been deeply dissected and the valleys broadened, another upward movement took place and the streams again deepened their valleys. This is the stage in which we now find the mountains. The crests of the ridges, characteristically displayed in eastern Pennsylvania, are portions of the first peneplain of which a definite record is preserved, while the broad valleys with sharply cut channels in their bottoms represent the much less complete second stage of planation. The two ancient peneplains referred to above, the histories of which are recorded in the topography, have received definite names in order that they may be readily designated. The older and higher one is termed the Schooley peneplain[2] on account of the preservation of a typical portion at Schooley Mountain in New Jersey, while the lower one, represented by the broad valley through which flows the Shenandoah River, Virginia, is known as the Shenandoah peneplain. A generalized profile in a northwest and southeast direction through a portion of the Appalachians is shown in the following diagram, which will serve to make more definite the description just given. The highest summits in the diagram represent portions of the Schooley peneplain; if the depressions could be refilled the surface of the great plateau formed by the elevation of this plain would be restored. The bottoms of the broad depressions represent the Shenandoah peneplain, which is sharply trenched by the modern river channels. [2] Also known as the "Kittatinny peneplain," but the name used above has priority. [Illustration: FIG. 17.--Generalized east-and-west profile showing relation of peneplains.] The Appalachians thus furnish not only a typical example of a mountain system produced by the folding and upheaval of the rocks of the earth's crust, accompanied in many localities by breaks or faults and overthrusts, but also preserve the records of two well-characterized peneplains. The long and varied history of the range has been in part interpreted by geologists from the character of the rocks, the fossils they contain, and the structure that has been impressed upon them; but some of the most instructive chapters are recorded in the topography, and their study has led to a highly creditable advance in methods of geographical research. The Appalachian Mountains when first seen by Europeans were clothed throughout with a varied and beautiful forest consisting largely of hardwood trees. Nowhere do they invade the region of perpetual snow, and glaciers are absent. These statements are true also for all of the mountains on the eastern side of the continent to the south of Hudson Strait.