Plate 1.—(a) Granite Weathering to Soil near Northampton, Mass. Under the action of weathering all of the once hard, fresh, mass of granite has crumbled to soil except the fairly fresh rounded masses which are residual cores of “joint blocks.” (Photo by the author.)
Plate 1.—(b) Looking-Glass Rock, Utah. The rock is stratified sandstone sculptured mainly by wind erosion, that is, by the wind driving particles of sand against it. (Photo by Cross, U. S. Geological Survey.)
Plate 2.—Grand Canyon of the Yellowstone River in Yellowstone National Park. The great waterfall 308 feet high is shown. The large swift river has here sunk its channel (by erosion) to a maximum depth of 1,200 feet during very recent geological time, and the process is still going on. The wonderful coloring is due to iron oxides set free during weathering of the lava rock. (Photo by Hillers, U. S. Geological Survey.)