Page:Popular Science Monthly Volume 45.djvu/200

  Map 1, showing the 500-foot and the 1,000-foot contours of the Ohio Valley; also the boundary of direct glacial action and the approximate limits of the slack water produced by the Cinicnnati dam. The figures give the elevation above the sea. Those along the river refer to the low-mark. In the lower right-hand corner is a typical section of the Alleghany, showing the rock channel and the high-level terraces.